Besides from owning the obvious (the gun), there's quite alot more to consider, really.
Safety equipment cost $$$, so does a pair of good boots.
At the moment to keep the cost low, you can go in as PMCs, but safety aspect shall not be ignored.
Just curious, have you been in a game before? If you have friends who's in airsofting, maybe you could ask them to loan you one just for you to try it out?
There would be two outcome from this.
1. You found out that it's not for you (very unlikely)
2. You love it more than ur GF (highly possible as they don't talk back).
You'd be surprise how one's newly gained enthusiasm can help you find more money. You'd even willing to work 2 jobs and eat bread for a month just to get the item you want.
Yeah, I'm on a long term bread diet. LOL