C02 seems like a stupid choice to even buy in the first place to me. Just get something electric and a smart charger instead of paying a buck for every mag you use up.
Electric isn't very reasonable for pistols. With the lack of space there isn't room for a standard battery like what is found in an AEG and you cant get very high FPS. Anything over 250-300fps is very rare for electric pistols, unless you spend lots of money. I think they both have their advantages, but I prefer C02 pistols vs electric due to the power.
EDIT: its also less than a dollar per c02 tank. Sometimes about $0.50
Example