I don't live in Budapest and have been there for clubbing only 2 times but I think I can help you out with some general info:
As far as I know, the biggest promoter group there is Bladerunnaz, --> http://www.bladerunnaz.hu/ they regularly organize parties, I've only been to their bday bashes they were nice... we had guests like Hype, Optical, SPY, Friction and june 7 it's going to be Noisia. They have a sub-group called Budapest Jungle, dunno much about that one but I think they're more into deep and old school stuff cause my impression is that the Bladerunnaz play mainly neuro and tech style dnb but I may be wrong.
There's also a crew called SheFire which is all-girls and non genre-specific, but DJ Ren (dnb dj) is a member and I think she's very good, if you're interested in her sound you should check out her page there she has links for her mixes:
Also Chris.SU is a Bladerunnaz member, I like him too, whenever I heard him, his sets & selection reminded me of Andy C: precise mixing, mostly fresh bangers but he brought out classic stuff regularly too.
As for the venues, I recommend A38, it's a well-known bar that's on a ship on the Danube, and I know that there were many parties in the place called Corvintető, I never been there tho.