I've seen pretty good prices at newegg (
http://www.newegg.com ) for dvd media in bulk.
If you want better quality media you will pay more. For good discussions on various media (cd/dvd) I'd suggest reading the forums at
http://www.cdfreaks.com .
I've read that the Ritek G04's are of better quality then most, generally when you buy these in bulk they come in a red wrapper (no spindle). I haven't had any problems with them, but I also recently got my burner so my experience is limited as well.