Blasting things the size of car bodies and frames requires both blasters and compressors that are way beyond hobby class equipment if you expect to make any real progress, or hope to ever do enough work to make it into a business.
The learning curve for bodies is real steep too. I've got a big Clemco blaster I've used more than I'd care to remember and there's no way I'd tackle a car body of any value until I'd first blasted half a dozen junkers to learn the proper technique. My Clemco needs a minimum of 200 cfm to run at low blast pressures, plus another 15 or so cfm to supply air to the vortex cooler that supplies air to the blasting hood. On a frame where you can jack the pressure on up, it'll keep a 350 cfm compressor loaded up pretty well.
Honestly, you could buy yourself a mid level bead blasting cabinet, a used home kitchen type oven, and one of the cheap powder coating rigs out there, and make some decent side money blasting and coating smaller parts. You could do it for little investment and with no worries about getting afoul of the regulatory mess associated with industrial type blasting.
There's a decent market for this type work because typical industrial coating operations don't want to fool with orders consisting of a piece or two of this and that. They'll either outright refuse the work, or quote it at a rate that'll make most people walk. Can't blame them for that, because their business model isn't set up on small volume work. OTOH, a guy who's doing small parts in his garage can easily spend a little while after supper and pocket $100 or more for the effort.
In contrast, the cost for a suitable bigger blasting rig and a used diesel compressor big enough to feed it would eat up $25,000 before you'd ever pull the trigger the first time. In addition, your blasting room would need to be more on the order of 20 x 30 feet since body blasting requires you stay well away from the sheetmetal surface to avoid wrecking it.
For the unfamiliar, big blasting might look like highly profitable stuff, but the reality is the operation itself is inherently expensive so the profit isn't nearly as big as it might look at first glance. Running a big blaster is fun for about 2 minutes until the WOW factor wears off. After that, its just plain hard work. I think you'll find guys like Shine and others here who do inhouse blasting as a part of their business will likely tell you they do it in house only to maintain control over the results as it relates to the remainder of their business. They probably won't tell you they do it because its fun, easy, or a quick route to riches.