Ones that come in big bottles LOL...
I found personally the cheapest way to attack murals (Large I'm guessing?) is to use a 4-6 inch paint brush for all the base color and some basic tonal variation in that color sequence..and do all those big slabs first, then the airbrush is really only needed to create more dimension or texture into that paintbrushed base or tonally change the bases color..
The reason I do it that way is its cheaper and with most murals I've done its been on a excrementty wall that needed a standard house base anyway, I don't really like using expensive paints as a base (BTW you can do that base bit with a mini HVLP Gun if you want the more sprayed look or indeed spraycans)..Also it really depends on the surface as well, how big your going, how much a client is willing to pay with various paint options, what the clients end expectation is...But yer hopefully some thoughts for ya..GL