Theres a number of threads on truk / chuuk in the pacific island forum.
Its hard to do on a budget - you first have to fly to Guam, then fly Continental Micronesia to Truk.
For land based operations its either Blue Lagoon or Truk Stop. From memory Truk Stop is a little cheaper, but they may have changed staff around recently. The thorfin was the cheaper of the liveaboards, but no idea if it has been repaired since hitting a rock last year.
Bring a good book - there's very little to do top side, and chuuk is not the most scenic of the pacific islands. Note email access for some of these operations is limited: its best to call them if you want to get quotes.
Its one of the best dive locations in the world, and I cant wait to get back there again next year.
Cheers,
Rohan.