If you are finding the price of BB's expensive, shoot less?
4,000 last me 2-3 games, maybe more... And that's a skirmish where I shoot lots.
The mindset of "Oh shit, I may not have lots of ammo" really helps tune your trigger/ROF
Every shot, becomes a precious little guy just waiting for that special someone
If you are finding you "need" to spray and pray, upgrade your gun for better accuracy.