Well...
Mainly field setup/reffing to be honest. Let's say you play an X Ball league with 10 teams in two "divisions" over the course of a year, with 4 regular season games, and possibly 2 "playoffs" games if you make the top two teams in your division.
Paint usage is 1.5-2 cases per player per game, so assuming the high end, you'd shoot 8 cases in the regulas season, and maybe 4 more in the post season, per player. That's probably on-par with what most people shoot playing NPPL/PSP 10-man.
So after that, it comes down to setup. If you're playing NPPL/PSP X Ball, it's $1750/team - same as 10-man, so an X Ball season is the same price as a regular season (or perhaps not, if they do two X Ball matches per event, in which case your paint consumption over the course of the season doubles. But after you factor in travel and all that, that's a small percentage increase, only about $80/event/player or less, depending on your paint and paint sponsorship.)
If you're NOT playing NPPL/PSP, then all sorts of variables come into play. Theoretically, you could play X-Ball on an existing 5-man field with minimal additions (lots of stop watches and some extra reffing) at a marginal increase over regular tournament cost, or you could set up a special X Ball field for your event, which would cost a lot more (although I've recently been informed of one way to DRAMATICALLY decrease the cost of running an X Ball event at a non-paintball location).
Anyway, point of the matter is that if done right, X Ball isn't much more expensive than regular paintball - most of the costs are in travel either way.
- Chris