Ok so because you claim that everyone that read this post realizes that his expectations are unrealistic, you have the right to criticize me for letting him know that and telling him what would need to be upgraded to achieve his said expectations? And your claims that playing at lower resolutions will remove a cpu bottleneck and higher his FPS is just wrong... If his CPU is keeping his FPS to say 25-30 fps if not lower, that won't change even if his res is 1080p (unless at 1080p his GPU becomes the bottleneck) or if its 1024x768 the FPS will still be the same or very close to.
So by getting a 1080p monitor he should be able to play the game with very close to the same FPS as he was getting before just at a higher resolution, but sustaining 35+ fps won't happen with his current CPU.
So as I said before get yourself a 1080p monitor but if you want your fps to to be 35+ you will need to upgrade your cpu/motherboard.
Here are a few monitors in your price range:
http://www.amazon.co.uk/BenQ-G2222HDL-21-5-inch-Widescreen-Back-Light/dp/B002UJ31A0/ref=sr_1_1?ie=UTF8&qid=1354131634&sr=8-1
http://www.amazon.co.uk/Asus-VE228T-Widescreen-Monitor-1920x1080/dp/B004OXZB6C/ref=sr_1_8?ie=UTF8&qid=1354131539&sr=8-8
http://www.amazon.co.uk/Asus-VS229H-Widescreen-Monitor-Headphone/dp/B005HIRFYO/ref=sr_1_1?ie=UTF8&qid=1354131887&sr=8-1