Select Family Video stores are having a DVD blowout sale at their locations for used DVDs. You can also buy new online but the used DVDs are reasonably priced. Check your local store to see if they have the sale going on.
I remember when 2 of my local Movie Gallery places went out of business. The crowds there looking for DVDs and games (had a pretty big video game library too) were insane. Are there actually decent movies worth seeing left at these things?
I have not had good luck with used DVDs in the past. They may seem like a good deal, but more than not they are damaged and do not work well. If a business is going out of business, you really don't have any recourse if there is a problem. What I do is find a couple of friends who have blue rays. We buy the double pack new, spiit the cost, and they get the blue ray and I get the DVD.
There used to be a Game Crazy and a Hollywood Video near me, and for like $1.00 each they would repair discs.