I sold my DVD collection a little while back and was intensely frustrated by the WIDELY varying prices offered by various purchasers.
So, I wrote a tool to do all the hard work for me by heading out to each of the popular sites, poll their price, find the best, and report back.
I just customized it into something I can share on the web that does one disc at a time, based on the UPC code. The form submits are all custom injected with curl, sourced from RAW capture between my testing browser and the purchasing sites. Enjoy the fruits of my labor 
If you have a ton of discs you want a report on, contact me and I’ll see what we can work out.
The site for the tool is:
and the sites it checks at the time of writing are:
EagleSaver, DVDPawn, SellDVDSOnline, SecondSpin, MightyBuyBack, and Abundatrade