with any big, common cichilid price is usually relative -- some lfs w/ a lot of room for big fish and that specializes in big fish might try and sell it for more money say 50-75$, however some stores see large fish as a nusiance and try to get rid of them for cheap, and will only take large specimins for free (or you might have more luck selling on a forum like this one to hobbyists who are into big fish)
keeping fish for a profit is almost impossible, unless you become an importer. I suppose if you could find a pair of something rare and breed you could pick up some change, but even pure bred labiatum do not go for much
This one LFS has this 180+ gallon tank with a bunch of Devils in there, asking $75. The store is over priced but the fish are always healthy and great looking.