What's a reasonable resale price for my iPhone 4 - 8g?

The phone is in perfect condition with absolutely no cosmetic damages.

Around 300 would be best

I paid £320 for my iphone 4 16 g and that was new unwanted upgrade and came with a 3 month warrenty. It was the handset only and this was a few months ago.
Just look on ebay averages
Envirophone and cex