Chris of Super5ives did this for Southampton Univeristy paintball society as a firing range etc
I don’t think you will find a cheap option, reballs bounce everywhere and I expect you will need to reduce the space used - especially if it’s a decent size university gym to make a safe playing area netted off etc.
If just as a practice range you could get away with gazebos and netting
You are going to need as many reballs as you can get because they need to be picked back up and cleaned before re firing