One of the first items you remove during the construction of a new racecar is the supplemental restraint system. Air bags. There also are a lot of other bits to remove, which you can sell on Craigslist to help offset a nominal amount of the costs of a new build.
Air bags are a tough sell, however. Because the first- and second-generation Miatas are so old, by the time someone might be in the market for a used air bag, their car is likely to be totaled by the insurance company. Last time I built a car, I tried to sell them, but they sat around so long I had to throw them out, which meant I had to blow them up first. This time, I thought I’d have a little fun with it.