How much is probly gonna depend on region, I payed $11.00 each for mine.
They are great fish, though IME they can get a little testy with each other. I had two that were constantly circlin' each other and flarin' their fins, so removed one of them. The other two now get along fine. 'Spect I may have two males and a female, and the two male were displayin' for the female's attention, but I can't find any definite info. They actually do a fair job of grazin' algae, as well.
WYite