It's always good to see a team trying to attend the Championship event. It's the best event FIRST has to offer, and the biggest.
As for your questions.
I know teams who have traveled from NJ to ATL by bus, and it just takes obviously an extra day for it to happen as opposed to flying. As far as costs, and things related to the details, it may be just as expensive as flying if you are renting the bus for the whole time you are down there.
The great thing about ATL is that once you get there, everything (and I mean everything) is within a 10-15 minute walking distance. The bus may not be needed during your time in ATL itself, so that may be a consideration.
As far as flying, it depends on the amount of people you have with you and how early you make the plans, but I know that both Newark and Atlanta are huge airports, so you have a large variety of flights/carriers to choose.
I would say price them both out with a realistic estimate of the number of people who will go and see what you come up with. Early is better than late, as the closer you get to the Championship Event, the higher the cost of flying.
(I tried to book a flight the week before, and it was about 1000 dollars from NY/CT to ATL) Needless to say, I missed the Championship event last year.
OK, Now for the wrap party. I'm not sure what the specifics of the event is as far as pricing/packages but my advice is this.
If you go there with the intention of keeping your team together all night long, save the money and just go out to eat, or just spend time together on that bus ride.. lol
If you are going with the intentions to meet new people, and having a little fun while you are at it and enjoying some free buffet style food for the masses, I would say go.
While the championship event wrap party is fun when you are on a team, the best part of it for me was meeting all the other people from the other teams in a casual non-competitive setting and having some fun.
So, if your team is antisocial, I would say do something together that night instead of going to the party. But, if you are all very social and want to meet new people, then go to the wrap party.
Hope this was some help.
As far as activities at the wrap party, I know there was some cool ones in 2004, but I'm not sure what was in 2005, or what will be in 2006.