Keep saving your money until your budget can stand a $4k gun. I know there's sticker shock involved with this type of purchase. But the quality of your work, the ease of operation, the money you'll save in the long run over a handfull of "less than optimal equipment" that WILL crash-n-burn, and the general lack of headaches will more than pay for itself sooner than you think.
Aside from having plenty of air for blasting, there's not much better money spent if you want to do this for $$$.
Bigger booth, bigger oven, sure, but no matter how big of a booth or an oven you fork over the cash for, it will never be big enuff. You get rigged up for 20' boat trailers, and somebody WILL show up with a 22-footer - EVERY time.
You can make more money doing small, custom work that will fit in a 4'x4'x6' oven, over a shorter period of time, with a good quality gun, than almost any coater around you can make doing oilfield parts, or 5000 widgets. The operating overhead for that kind of work is staggering...........the profit margin is pitiful.
If my competition could do what I do, then I'd have some competition.