First of all, all Modifications for Half-Life & Half-Life 2 are free. If they are not, well. They would get a few problems on their road. Secondly, there are Half-Life 2 Dragonball Z modifications, but they have not been released yet. Such as Dragonball: Source and Dragonball Adventures.
I don't think there are a lot of Dragon Ball/Z/GT mods out there, or at least ones that are still active. The only ones I know of that are pretty active are the ones coming out for Source and UT2004 (plus ESF) and that's about it.
There's one.... Bid for Power... Its like ESF but for quake... although its not anything near esf, its a good start off on such games, easier for noobs.... but trust me, BFP is worth playing only till you know you rock.... Its lower graphics, no good voice... the game is old, for heaven's sake... take my advice... ESF is the bomb!
PS: dbz hood is gonna take forever.... or it looks that way. By the time it comes out, you'll have Tenkaichi 2 for PCs...