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Koyote I'm a math teacher, and one of my capstone lessons when I taught Algebra II was doing the math on why you don't buy a car with a credit card. Of course, we assumed making payments, not paying it off.
Basically, if you are cash-rich, reward cards are legal money laundering. Bank of America recently 'improved' my cash-back card to a travel points card, and I think it was because they were getting sick of all the money I was getting. I'm in the process of switching it back, which is amusing (if I'm successful) or potentially frustrating if I'm not.
Mortgages really can be a source of unexpected deals, too. For having a combo of qualifiers that were as simple as direct-deposit, a 700 FICO score, and $2,000 in checking, BoA gave me a 3.875 mortgage with 10% down (I bought in '08, and did NOT want to sink money into real estate, regardless of whether I lived in it). That saved me about $40k, when all is said and done.
Re: bikes, there is no way to make small-volume goods to compete with the price of mass production. Not trying to be a jerk, but that's kind of high school economics, right? The $150 worth of welding done on a $4k bike isn't done on a part-time basis by the welder; you need to keep him employed, pay benefits, etc. "Overhead" and "Cost of Sales" are two very misunderstood concepts for many people.