one draw back of "classic" airsoft is the air system. now assuming they run on hpa you require a way to refill. how this is done is by cascading multiple scuba tanks. right there is a huge expense as 90% of airsoft games dont have anything like that... gta may be different considering you guys play on paintball fields...
another thing to keep in mind is any refillable high pressure vessle requires a hydro test every 2-5 years depending on the material its made out of.