Go to everymac.com, click the lookup button in the bar at the top and enter the last 3 or last 4 of your serial number. This will give you your exact model specs and lots of information about it. Look for the model identifier, it will be something like this: MC700LL/A
Take that and do a search on sold items on eBay and look for ones in similar condition to yours and you will get a range of how much it is worth to an eBay buyer. Local cash sales are usually 15% or so less than this price.
By the way, there are 3 MacBook Pro models in 2011 with 2.3Ghz processors, a 13 inch, a 15 inch and a 17 inch so I would need more information to go get you a price.