I doubt S+ grade CRS's are 5 dollars. There's one LFS in San Diego that sells CRS for 6 dollars each, and that is for a low grade C or a B CRS. 3 dollars is a good price, I'd say.
I think it's a decent price as well. The great thing about buying lower grade CRS if you're on a budget is the fact that when those lower grades are successfully breeding, it's most likely that you will end up with some higher grade offspring because the genes are all there. If you want to get serious, that's when you start to cull/sell the lower grade babies and then purchase higher grade bloodlines to strengthen your colony. Good luck!