Knowledge is definately a must for keeping seahorses. I can emphasis this enough, but research, research, research, and then when you feel like you have a grasp on it, research even more.
Totally agree that true captive bred ones will most likely give you less problems than a tank raised or wild caught specimen.
As for price, depending on species or whatnot, $40 is reasonable/cheap for a seahorse at a lfs, which probably (not definately, but probably) means they are wild caught or tank raised. I paid $75 a piece for my four reidi.