I'd suggest checking eBay - search your specific model. Then, look in the left hand column on your screen for the words "More refinements ..." Click it. In the window that pops open, at the bottom of the left column, click "Show only." Then click "Completed listings" and click Go. Now you will see what MacBook Pros like yours actually sold for on eBay.
You can also get quotes from many of the online Mac resellers (for example, MacOfAllTrades) ... but they will only offer a price more like "wholesale" because they are in the resale business.
Third thought, if this is truly a like new, barely used MBP, you should be able to sell it for 80% or more of what you purchased it for. Macs hold their value pretty well, especially if they are recent models.