Gyarados' fin:
At the end of the 500 Gyarados' task, I had looted 100 gya's fins and 64 gya's tails, so it's almost as hard to loot as the tail and it's only 18 dollars, while tail is 2 hd each. Increase its price to 0,8 - 1 hd.
Clefairy and Clefable's tail:
You can sell both for 50 dollar...