IMO, I'd spend the extra few dollars for a semi. I've played with both, and as an amateur, I can say that there's a huge difference between the two. I constantly gave up so many opportunities for kills because of double pumping in the heat of battle and fouling the bore. It can't really be that much more, and if you plan on playing more than once or twice a year, you'll be happy you started with the semi. Like Papakeith said, you can get the kit which comes with a tank (very economical over the long run). And the last two times I played, one tank lasted through 500 rds (used over the whole day).
What we do (my unce and friends) is rent guns, takns & masks for the day. 8 of us, plus 500 balls each, and the cost is under $50 ea. I'll continue to do it this way, as I don't know anyone else who plays (hint- any DRn'ers out there in Central Cal who play recreationally?).