To clarify: I know for a fact many of the crew worked on Star Wars movies for example. Adam specifically worked for Industrial Light & Magic. One doesn’t come by talent like that with only chump change to offer, so I suspect they were at least doing pretty well before even starting Mythbusters.
I’ve known a couple of people who worked on Star Wars and other big movies. You get a decent wage, as anyone who works in movies does because it’s such an unpredictable career not knowing where or when the next job will come, but for anonymous crew members it’s not as lucrative as some people seem to think.