I really think it's important to stress how slow of breeders they are. I started my colony with ~100 roaches, maybe 20 of them adults. It took at least 8 months or so before most of the second generation started reproducing. A year and a half later, they measure in thousands, but it certainly took a while to get here. They're also hungry little buggers. Out of curiosity, what is "cheap"?

For comparison's sake, I gave away all but ~30 red runners last September. They're currently well over a thousand strong despite me "accidentally" forgetting to feed them several times a week. Within a couple months they should surpass my dubia colony yet again. Being as that was the fourth time I got rid of almost all of them, you can see how they vastly outbreed dubias. A few dozen domestic crickets could potentially surpass my dubias in only two or three months.

tl;dr: You won't end up with more dubias than you unless that's what you're trying to do.