I wouldn't go much bigger than 1280*720 as far as resolution. That will get you 720p HD and you are have to sell your organs to get up to 1920*1080.
I also bought a 21" monitor at staples for 70 dollars at Christmas time. It has a 1920x1080 resolution. Right now I think it's 140 or 150. One of the cheaper monitors they have.