Some people use minerals and gas for vhp, well kinda annoying so i was sitting around thinking about things and thought of this..
Player gains a level add a death count to player, bring player brings unit to building give to player add a timer say 35 - 40 seconds, upgrades are free but on a settime limit, say weapon 15 - 20 while armor like 10 - 15 depends on person. Once all done subtract the death and give building back.
this doesnt require money or gas for person upgrade so you can then use money / gas for other things. anywoot enjoy.