Assuming you’re talking about Rams (Mikrogeophagus ramirezi), no, you will not likely find them in Petco or Petsmart, mostly because they can’t keep them alive long enough to sell. You’ll either have to look at privately owned stores, or even ordering online. They’ll cost anywhere from $5-15 depending on quality, size, and what they’re eating (fish eating pellets will cost more than fish eating only live food, as they’re more desirable). They will definitely NOT eat other fish under any normal circumstances, nor should you encourage this. Males will spar with each other, but they will rarely do real damage (other than to their egos). Really, if you have any hopes of keeping more than one, you should have as many plants as possible, and several pots or pieces of wood for them to establish territories around. Height? It’s not really a statistic of any importance here, but they’ll get about an inch tall without the fins, and 2-2.5″ with the fins. The only time I would suggest keeping 2 in a 10 gallon tank would be if they are male and female with NO other fish in the tank, except maybe a school of Danios. Weekly water changes, frozen or pelleted food, 80* water, and that’s about it.

EDIT: Luckily, everything but the price is just about the same– expect to pay about $10-20 per fish.