well if you want cheap cels junkjungle.com 
has some SOMETIMES of DBZ right now theres only 
Genga/Douga(Production Sketchs) etc.

Ebay has TONS of DBZ cels but they are really 
relaly Expensive..

you just have to kinda look around anime-cel.com 
has some GT cels for resnable prices.

Er..I don't really know much on DBZ cels other 
then that sorries i tried:)