I bought a Milwaukee sprayer from HD for under $400.
http://www.milwaukeetool.com/tools/...choices/airless-finish-paint-sprayer/M4910-20
It excelled for spraying primer in a new construction home with no flooring down. Once I got past that point it lost it's utility for wall painting. It was just too much hassle, and doubly so if you have a lot of different colors.
Where it worked well was spraying my doors. I set up a shop in the basement and went to town with it. The key I found was humidity. You *can't* spray in high humidity. It just doesn't dry fast enough and you'll get runs. The drier the air the better off you are. And paint type makes a huge difference too. I used a flat black paint for my theatre room door and it looks like it was painted in a factory. It was flawless. The white "trim paint" that I used for the doors was Dutch Boy mix that was very difficult to get down right. I spent a lot of time sanding down my screw ups and repspraying. Most doors look decent, but a couple of them are pretty bad. I really need to take them down and sand and respray. They are still better than the lines you get even using a foam roller though.
The sprayer also plowed through 600 feet of quarter round in about 30 seconds a pass. Seriously...it took like 4 minutes of actual "painting" time to paint that stuff.