My average so far for the past month is $26 while playing 2x (Every other week). Fills are free for me since I supply the tank to our recball players. The $26 was for a box of 1000 PMI premiums and I still have 400rnds left. Sunday I took down 1/2 the enemy team (2 players) with 6 shots from my PGP. I nailed the first guy with one shot.
I seem to do better the less paint I use for some reason. The 400 rnds will probably last me another month since I've still got plenty of 10 rounders filled for stockclass. Once you are happy with your setup the only big fee (field and fills are cheap) would be paint. You can really save some money by aiming.