Hmm well for a decent LCD monitor it can run you some where between $120-$190
Cheapest 1080p monitor (1920x1080 resolution) I could find on Newegg:
http://www.newegg.com/Product/Product.a ... 6824009264
My system is:
Intel E5200 @ 2.5GHz (aka worst/cheapest Dual core intel makes)
4GB of RAM
and Vista
My system cost me $300 bucks clearance and I love it. Runs smooth as a whistle. I do every thing but serious gaming and I do it with out a problem except it (video rendering, multi-tasking) will take me longer than the real powerful systems. But I demand a lot from my machine and it is with me 100% so if your just browsing the web and email than your biggest issue will probably be the choice of OS. Even cheap hardware can handle easily handle what the web as to offer, you just need to future proof yourself with the most current operating system you can get your hands on (Windows 7).
Hopefully that can gauge you when it comes time to purchase your desktop.