Rad - for a 10 gal tank you can go to Lowes or home Depot and pick one up for about $20.00... that wouldn't last you long though, probably enough to do half a models worth of painting though so if you have a source to refill them close by you'd be set.
... someone spoke of them having 30 gal tanks which would last you awhile I would think... I havent noticed them there yet though... (at the hardware stores)
You can also check with the local compressed gas people (not sure what they would list under inthe phone book) and get a C02 tank too... just bring it to be refilled now and then, some people here use C02 to airbrush, and go as much as a year without refilling. Thing is with those they rent them so you would need to find out the rental fee....