Well you said the magic word.... DVDs....
here are some links to start you off
http://www.dvdpricesearch.com/ (best place to do compare prices for dvds)
and
http://www.deepdiscountdvd.com (cheap prices only "problem" is slow shipping, but the slow shipping option is free)
I will also recommend resellerratings for any website/store that you have never heard of.