A 900 dollar computer and a nicer monitor is well worth it, because spending 1100 dollars on parts to play on 1280 x 1024 is kind of pointless. It would honestly just be overkill to have an HD 4870 on that resolution. The best move is to have a good balance between the resolution and pc hardware, or less you'll be wasting money, because you either won't be able to play the games at that resolution, or you'll have spent more than you had to in order to play at the same resolution.
And 900 dollar custom built computers still kick ***. If you get a nice monitor with a 1680 resolution or something along those lines, you'll be able max out games at that resolution, as opposed to maxing out games at 1280 x 1024 without even working your pc.