It sounds like he's being a dad (am one myself) and not letting you get into something that he's afraid you're going to make a disastrous mess with.
Basically when you're airbrushing you're merely making an oversized can of spray paint that gives you control.
GW compressed air (and similar types) offer the same flow as a can of spray paint.
So here's my question to you, are you doing this on a base coating level or are you attempting some detail work on vehicles? If its the former then the
GW airbrush with a couple of cans of propellant will cover you just fine for around 50 dollars initially. Buddy of mine did 100+ models with two cans.
The other thing to keep in mind is that airbrushing will go through material much faster than hand painting. The waste is reduced if you're doing detail work or bulk base coating.
I don't think I helped much