Went to my local Harbor Freight "parking lot sale" this morning (it was held inside the store, partly because of the weather, but mainly because the jerkwater town in which it is located [Sugar Land, Texas] doesn't allow parking lot sales because they sully the ambiance and patina of the town and people milling about buying things is vaguely unsettling).
Anyway, HF is now selling a fill-it-yourself aerosol spray can
You put whatever you want to spray in the can (paint, mustard, deer urine, etc.), and add air through a bicycle-type air inlet - either from a compressor or hand pump (90psi max) and you're good to go.
I got one and may use it someday. When I do, I'll report the results. I also bought a 1/3-sheet electric sander for $19.99, which I WILL used today. I've got to remove about 87,000 bumps from sheetrock texture in advance of covering the wall (13x8) with a mural.