A number a factors can effect the price you think is good for any fish.
1. Picked up or shipped.
2. Size, age and sex.
3. Rarity- how common in the wild and how collectable. Can they be farmed and/or tank bred?
4. Availability- how difficult to find for sale.
5. Health/condition. (One healthy fish is worth at least 3 or more dead ones.)
And then after all of the above, how badly do you want it, how much is it worth to you and can you afford that? Everything is relative.