How to mess QC probe on a bunch of DVDRs

I got a feeling that some of my DVDRs is degrading. Therefore i needa to do a QC scan on everyone. I got 50 over of them… But i have no idea on where to start…

What dvd drives do you have (makers/models)?

Do you have any money to put into this scanning (i.e. can you do it professionally by a 3rd party)?