Good question, I've bought quite a few 'used like new' from Amazon sellers and until recently been pleased with all but a couple, but been royally ripped off with enough ~recent orders to back away for now, so been on the lookout for other options. Amazon has been a bit of a 'mixed bag' about helping with getting some satisfaction, sometimes with an 'over the top' resolution, especially where packaging has been the problem, and some completely ignored, so like most things, 'caveat emptor' applies.
In my locale there's a fairly large used bookstore which sells used LPs, DVDs, BDs, etc., and for the most part all DVDs are $6, BDs $8, but historically virtually all my DVDs, BDs [whether new or used] were bought for less [many for much less], so if you have the time to follow/search the seemingly myriad sales on-line and in stores as well as take advantage of Best Buy's periodic 'upgrade & save' sales, averaging ~$5 [or less] over time is doable.
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.