Below are a list of fossils and their prices if you sell them to Nook.
Fossils are worth a little or nothing. until identified by Blathers at the museum.
1800 bells
about 19.99
2,500 bells
15,000 bells
1000
All gyroids are worth 828 bells
If you look in the Animal Crossing Community website, they will say that you will get 2,100 Bells if you sell a gold rose.
You should be able to trade it in or sell it for about $15.
A peacock is not an obtainable animal. If you mean the peacock butterfly, about $2000 bells.
500 (huh!) yeah, whatever... (sorry about my sarcasm)
$39.99
You can find a list of all the bugs, how much they sell for, and where and when to get them at this site: http://accf.wikispaces.com/Bugs