Best place to buy used ds?

I've been finding places in the area,like the library a dollar each...fot single or double or box sets.A thrift  by me they were 5 for a Dollar come on 20 cents each thats nuts all in nice condition. 

+1 for Discogs, which is my go to online store for hard to find discs. Locally, I like to shop at Silver Platters at their huge flagship store in Seattle. They also have a website which you can shop online.

https://www.silverplatters.com/

I buy them for 3-4 bucks at my local record store.  If you have a half-price books store near you, they usually have a large collection and here at least, they are typically 3 bucks.  They also sell online.

Best bargains are charity shops, or second hand record stores in their cut out bins.  Also if libraries have sales