How big of a area do you want to spray? I use disposable Preval spayers for gel coat spot repairs, and also have used them for spraying bigger areas too. They are $4 at homedepot and can spray up to 16 oz of anything you put in the jar. You can buy them with the jar or just the power packs alone. You can also clean them up easily and re-use.
If you want a real gun then just get a cheap harbor freight paint gun and drill the tip out a little bigger(or buy a bigger tip).