As mentioned before...if you are just painting mowers, a touch up gun can waste a lot less paint...but then again, a touch up gun is not a good idea to try and lay clear coat on a panel, especially for your first time spraying. Their is an art to clear, it is not as easy as everyone says. If a guy tells you ' I don't run my clear', he aint puttin enough on for that super sweet look!!!
As far as guns...we had an 89 dollar napa gun, was pretty good. But the Devilbliss we have, is absolutely top of the line...it is THEE nicest gun I have ever used and I've had my hands on a few. But you get what you pay for...at 500 it wasn't cheap, but they have a cheaper line as well that I'm sure you will do fine with. A lot has to do with tip size as well...I spray filler primer through a 2.0 tip, sealer and paint through a 1.4 and clear through a 1.5. All have totally different abilities and purposes.