Whatev, demo's plenty cash-efficient if you're not shooting/throwing nades/dropping pipes everywhere unnecessarily like a tool. Speaking from rank 5/6 on hard/suicidal.
You don't have to kill everything yourself- it's a team game: shooting 1 nade-launcher round to weaken a crowd of gorefasts enough to be killed by 1 bullet a piece from a teammate is very ammo & cost efficient for the both of you.
I'll give you this though: for the piss-poor damage they do, hand grenades are blasphemously overpriced.