$400 to $450 on eBay or local. Accessories can push it higher. Sell it local and have no fees to worry about or risk of forced returns. Meet in public, cash only.
I'd recommend using the free estimator tools at CashForYourMac.com and MacMeAnOffer.com. You may like their quotes enough to go with one of them too, but if not, at least you'll get a reliable value. Both companies are well respected and recommended by MR users.
You can also take a look at Swappa.com to see what other devices like yours are selling for.