Sounds very similar to the old "Long Night" mod, remember that?
A custom designed map with a script enabled to allow players to follow certain objectives would be better then just mowing down “zombies” continuously.
End of the day it’s the accreditation from the public that matters most instead of a few quid’s worth of money.
Everything that’s happened to me just by being a player, a £5 note isn’t too bad to credit for.