To illustrate my point, compare a $65 eBay trainer to a $375 fluid-trainer with computerized power meter... or a Walmart-grade bike carrier to a THULE. There will be no comparison.

Generally speaking Speedplays have been very carefully engineered to prevent cross compatibility between their products.

When I made the switch, I had two pair and I wanted another. It was the used market or a switch to SPD-SL. I ran two pairs of shoes for a time before I found some gen-1 SPD-SLs for cheap to re-equip my stable.

You can thank me later for contributing to the used market so you didn't have to make the switch.

It's not a cost % thing, it's a total cost thing. I don't want what started as "Hey, I can build up this nice old Davidson frame someone gave me for $50 + stuff I already have" to turn in to "I can build up this bike for a mere $400 in additional parts". Now I generally do just buy the item, but then again I have a full time job. Back when I was in school full time eating and buying books was more important than buying a pair of $100 or $200 pair of pedals.
It should also be noted that while the absolute cheapest option rarely saves money, the next option up often does. $15 brake pads (car) suck, but the $20 ones last as long as the $60 ones, and stop more than well enough for street use. Example, my commute is roughly 65 miles each way (long story, don't regret it). I could buy a recently used Honda Civic with 20k miles on it for around $15k. On the other hand, 5 years from now when the SO finishes her PhD I would have a car with between 250,000 and 300,000 miles on it. On the other hand, the $1 car (from a former room mate, could probably buy one for under in equivalent shape) consumes ~$500/year in maintenance (oil, suspension, tires, light bulbs, whatever). The insurance is lower, the fuel is the same. Because I do my own maintenance (It's actually a stress reliever for me) I'm way ahead.

This is true a lot of the time...

IE, don't buy the cheapest bike shorts you can find... buy the higher-lower end or lower-mid-range item (or buy the top-of-the-line bargain brand, like the $60 10-panel shorts from that website). Although to be honest I don't think my slightly-above-the-cheapest Cannondale shorts are going to last all that long, plus they don't have enough padding on the sit bones. The reflective accents started to peel off within weeks of use.

As far as components go, don't get Tiagra, get 105... don't buy a $25 Walmart helmet (...seriously, don't... they have ZERO cooling and don't have stickers you need for the racing/tri!), and you should probably avoid the $40 LBS helmets... so buy the $60-90 model unless you crash a lot and have to replace helmets constantly. Otherwise you'll end up being out 25/40 dollars when you decide that your helmet doesn't cool enough (or at all), doesn't fit well enough, and isn't aero enough and buy a better one.

And when it comes to installing those $20 brake pads, do it right the first time instead of having to redo it or take it to the shop.

I'm sorely tempted to buy a Sette/Welgo pedal combo off PricePoint (the cheapest one they make is only $80!), but I'm 80% sure I'm going to regret doing so if I do, and you should usually go with your instincts because they're right most of the time.

Then again, I've heard some fairly good things about the $130 carbon fiber model with the SPD-SL-type pedals, but it's surprisingly easy to make something that looks so similar not work nearly half as well. I know that even if the shoes fit me, they're probably going to wear out and fall apart faster than the mid-level shoes that Specialized or Pearl Izumi make, and that the pedals are probably going to need to be adjusted much more often and will wear out in a shorter amount of time than Shimano or Crank Brothers pedals will.

...but $130...is still so tempting.

Two pairs of pedals is most convenient. BUT, if you are patient and competent, you can use one pair of pedals for 2 minutes of work each time you transfer your pedals between bikes. On avoiding cross-threading, go by feel. If, when installing you feel "this is too much" resistance, just back out, and reposition. DO NOT FORCE the mount. Today's machining is great, things fit together nicely.

I switch out pedals all the time, no probelmo. Before applying the wrench, use your hand. If you can do can do the installation by hand until you reach the end and need a wrench to lock it down you have the threads lined up. If you are cross-threading, you'll get stuck using your hand after 1-1.5 turns. Oops. Even if you use a wrench earlier you can tell whether threads are mating. If it's smoothly turning its good. If you find you are exerting serious force, back out and start over.

Because R&L threaded pedals are designed to not unscrew under load, you don't have to wrench very tight. Give it a little noodge at the end (15 ft/lb torque) and you'll be set, and you won't have to use a mallet on your wrench handle to loosen the pedals.

Cross-threading and f***king your stuff up is the product of haste and/or basic mechanical incompetence.

Sheesh. Swapping pedals is no big deal. I've been riding a long time, and it wasn't until last summer that I finally had a pair of pedals on every bike.

Grease the threads, finger tighten after making sure there's no debris in the threads, and then don't overtorque when you use the pedal wrench. It should take less than a minute. There is no danger in swapping out pedals hundreds of times.

If you swap pedals, you can always ride the good ones. If you have 4 or 5 bikes, the amount costs to stick pedals on all the bikes could easily buy something else you'd rather have. The other issue is that if you're not 100% sure you have the best pedal system for you, it's much easier to switch if you have fewer pedals.

I actually lol(ed)

I got multiple bikes, typically just get $12 pair of pedals to make a bike rideable if there are no pedals. If you really need to clip in on both bikes, do some temp work on the weekends.

Reminds me of when I only had a mountain bike and thought it would be smart to have slicks and knobbies and swap tires. No way! Then I got two wheelsets. That didn't even work for me. It takes several bikes ready to roll at any given moment.

I got my Mongoose sitting around with no pedals ATM, cuz I bought another bike for $18 that had foobared pedals, and I wanna sell it. I swapped pedals between it and my KHS a couple times, but no more.

Good points.

My beef is that the cost of pedals really isn't that much. If someone says they can't afford pedals, they either can't handle their finances at all or they must be posting from the public library or homeless shelter because they can't afford to pay for internet, a bed, or food either.

Get a pair of platform pedals. A lot of bike shops will basically give you used ones. Maybe put power grips on them. Then, if you want to go for a short ride, you can use that bike and whatever shoes you want. If you decide you want to have the clipless pedals for a longer ride, swap them.

By the way, this is pretty much my set-up, although I never actually swap the pedals. Candy C's on one bike, touring platforms with powergrips on the other (commuter). I have mountain bike shoes that I use on both bikes. The cleat is recessed enough that I don't notice it on the commuter, but it's still nice to have a stiff shoe. The power grips let me use hiking boots in cold or wet weather.