I actually have 5 sprayers, but onlt 2 are used for spraying my models
The Airbrush and the Touch up gun
You can use a air brush to paint any size plane, it just takes longer, I use the air brush mostly for Camo and detail work, where small amount of paint are required,
For larger single color areas I use the Touch up sprayer.
The touch up cup hold about 10oz of paint

You can get a airbrush for around $30-$40
and a Touch up Gun for about the same
All you'll need is a compressor

BTW they have at harbor freight

That wagner gun you mention is junk even for just painting your house