Nobody wants to give advice to a lawyer; it's too dangerous to be wrong

You might be able to find a deal on a used bike. It depends on how much know-how you want to acquire, which means time you want to spend before buying. Sometimes you can find an $80 5 year old bike that street-prices for $300 and it's ready to ride; sometimes you find a $150 bike that street prices for $250 but it's horribly beaten and needs new gears/chain/etc and you wind up paying $350 in total.

You pretty much have to be a bike mechanic and a strong negotiator (being a lawyer, I'm sure you're good for the latter... or you suck as a lawyer, one of the two) to guarantee you're not getting screwed, even buying a brand new bike; the closer you get to both of those, the more money you save, obviously at the cost of time investment. Plus, with decent enough technical understanding of bicycles, you can completely skip paying any mechanics to work on your bike, ever, and STILL keep your bike in better working condition than with regular tune-ups (because you do them whenever you feel like it, rather than on a schedule that compromises versus money).

In other words, it's dollars versus time. You want a great bike? Drop $2000. Or you could spend a month bouncing from store to store, reading up on bikes online, test riding, get some vague(!) idea of what makes a good bike, then drop $500 on something you're confident is a good bike. OR spend months and months learning about bicycles enough to go find a $50 broken one with a great frame in great condition and swap in $100 of brand new parts to make a great $150 bike.

At a point, you're wasting your money. Buying a First Act guitar or a really crappy $100 off-brand budget guitar will net you something that'll never intonate right (i.e. ALWAYS out of tune, physically impossible to get into tune), always have high action (difficult/impossible to play), and never really have a great sound. A $2000 Taylor is awesome; but there's great $300 guitars out there that just freaking rule, nowhere near on par with a $1200-$5000 Martin or Taylor but they are just amazing.

It's the same with bikes, really; that doesn't necessarily mean you're going to completely hate a $100 Wal-Mart bike, but there are plenty that will teach you that walking is better.

One thing I found out when I bought a $450 bicycle: brakes are awesome. Every Wal-Mart bike I owned had rubber V-brakes that slid and skid... not much stopping power, never could lock up the rear wheel. A drop of water on the rim disabled the brakes. These linear pull brakes with Shimano pads, though, they'll stop my wheel dead from 15mph in the rain. That surprised me; I seriously considered disc brakes because I had bad experiences with rim brakes.

Lessons learned? Spray the rim/brake pads with a water bottle and see if you can still stop the bike. Do this to one wheel; use the other as a back-up if it totally disables the brake. If it does totally disable the brake, don't buy that bike! Wal-Mart may be using improved brakes now, so maybe they can stop you when wet.