It definitely depends on how available certain characins are, a flame tetra could be $2.50 while a super blue kerri tetra could be double that. Still pretty cheap, but when you're buying a group of them, it adds up. Usually, a juvenile angelfish without special genetics will go for $5-7. If you're buying 6 angelfish at 7$, that's $42 and a group of 15 cheap tetras is roughly the same cost.