most fancy goldfish are fantail type goldfish. Fantails have 2 tails, whereas common and comet goldfish only have 1 tail.
Fancy fantail goldfish are available in common fantail, black moor, ryukin, pearlscales, bubble-eyes, orandas, ranchus/ lionheads. The breeders are still messing around with the breeds and trying to make new ones, but those listed are the most common and should be available from most shops.
Depending on how big the fish are will determine the price, also where you live will have a bearing on price. In Australia prices are sapproximately
Small 1inch common fantails or black moors should only cost a couple of dollars, whereas bigger fish (4inch) will cost $15-20 or more.
Good quality ryukins about 1inch will cost $10+ and 4inch ryukins can cost $50+.
1inch pearlscales and bubble-eyes will sell for about $10, 2inch fish will sell for about $20ea.
1inch orandas and lionheads will sell for about $5, whereas 4inch fish can sell for $30-40.
All the fancy fantail goldfish can reach 4-6inches, some (ryukins, black moors and common fantails) will get bigger, perhaps reaching 8inches in body length. Pearlscales are the smallest and only reach about 4inches long.