Assuming this is a RBC, and given there is no reason for a premium on cut or brand premium, this should be available for 20-22k for a good deal going to 30k and above for special cuts and pretentious stores. In this (rather large) price range, it is up to the buyer to select a deal and decide what the stone is worth to HIM, since small increments in price do not necesarily reflect better quality.
Those in the know say to be careful with IGI lab reports. This seems especially true with a D VS stone. If it gets knocked down to E SI1 by GIA then you might be talking WAY under $10,000 per ct. Be vewy vewy careful!
Resale value, if that's what you are asking, is a different matter all together.
Do you mean, how much did he pay/how much should I have paid? Or do you mean, how much could I resell it for?
Also, the stones DEVO were looking at were GIA certed. IGI is less reputable and tends to grade more leniently. The GIA might have graded your stone as E VS2. In that case, comparable stones are going for $17500-$23700. If you are looking to resell, you will not command a price in this range -- people are willing to spent that much at a reputable establishment that has a vested interest in keeping them happy and can provide service and upgrades. People will only buy from an individual trying to resell a ring if the discount is so great to make up for the loss of security/service and/or if the stone is what they would have chosen for themselves to begin with.
An IGI 60/60 type stone with a thick girdle? Hmmm.....if you were buying this...similar diamonds online are going for around $19k but that is GIA certed...so may be more like $17-18k for this one with IGI.