well if you want the best.. i strongly recomend you to get a wild pair, that way you will save a lot of money in food and water changes and time threw these years.
but if you enjoy seeing them grow with no aparente results like me, buy them at what any size you can.
a fair price for 1'' is $8 so get them.. i buy 2 of them at 1'' and 1.25'' at 8 each, 6 moneth later they are 2 and 1.5 and i didn't notice until i introduce new fish in the tank.
calvus are onely in three colors, black, white and yellow beeing the yellow more rare and a little more expensive.
gold, orange, black and red are compressiceps variants.