One of the biggest differences the higher priced models offer is the ability to operate more than one spray gun at the same time.
Also, the amount of usage is important to consider when buying a sprayer. If it will get daily or heavy weekly usage, than a higher grade model is indicated.
If only light or personal usage, than a lower priced model may well suit the bill.
It is also important to understand the appropriate spray tips that are used for differing materials.
Ease of clean up is nice to consider, because if it ain't easy to clean, you aren't going to like using it.
I only use a sprayer 5-6 times a season, so my Graco Magnum 7 sprayer from HD works great for me.