When I figure out how to sell an item, I go to http://www.ebay.com
and find out what the going prices are currently on an item.
To save time, I just searched for eBay keyword "Unlocked 7230" with the Completed Listings checkbox enabled, and noticed the prices hover about $200-$275 USD.
As a result, I recommend offering a price in that approximate range, perhaps $250 for local pickup if it is in excellent condition with all packaging. Hope this helps!