*About the Zebra Plecs*: I doubt you'd be able to tell. I've seen some tank-raised zebra plecs and they're just as gorgeous.
*Sati*: William is right that rarer, harder-to-breed fish are more expensive, but don't let that make you think that you'll make more money if you breed them! Fish may be cheaper if they're easier to breed, but you may be able to breed 100 or 1000 times as many guppies as you may zebra plecs. In that time you may have made $100... and you may not have had to put in any effort at all!
I find that most small-scale breeders tend to stick with rare species, esp. discus and fancy plecs. They simply can't compete with large farms where fish can be produced quickly and cheaply in bulk, or with fishermen who can harvest these fish from the river even more cheaply. So, I would either go with guppies (nice and easy) or consider setting up a serious breeding tank for nice plecs. Not much point in trying to breed neons, serpaes, gouramis etc....
*Illuminum*- your 30 is overstocked, or will be real soon!!