Price Advice Custom rMBP value?

Hi,

I'm going to sell my Late 2013 15" Retina MBP. My problem is because I had it spec'd out at purchase, I don't know how to value it.

I paid £2,200 in October 2013 for it. It's absolutely mint condition - Apple have just replaced the screen enclosure (due to a creaking hinge) so it's like new.

• 2.3 Quad Core i7
• 16GB RAM
• 512GB SSD
• NVIDIA GeForce GT 750M
  
• Intel Iris Pro
• Box in mint condition
• 2x chargers
• Applecare until October 2016

Any idea how much I should be looking to get for this? I'm in London,UK so a £ value would be very helpful!

Thanks