Jawburger & Sandmail, thx you both. I'm looking through the classifieds now and there are plenty of deals to be had. Blu-ray.com is also great and the sort by price function there is useful. I had no idea that new 4k movies could run as little as $10-15 (I figured anything 4k would be in the $20-30 or more...but I'm glad I was wrong).
I've had great experience with the AVS Classifieds and Newbury Comics.
I looked at OfferUP and that seems to be a great place for DC codes however, when I noticed someone selling a HD code from a 4K disc and let them know they didn't change the ad. So, there's risks anytime all the time.