That is a good deal, considering I sold my iPhone 4 for like $220 off of eBay. I would consider selling it on eBay if it's in good shape. Mine was in a decent condition, just a little chip on the outer ring of the screen.
An iPhone is an iPhone at the end of the day so it doesn't really matter as long as your happy with it. I think you've grabbed yourself a top-notch mobile phone. Congratulations.