For the usage you described, any modern cpu will do.
I might suggest a Celeron g1610 for $50
http://www.newegg.com/Product/Prod [...] 819116889A
A H61 motherboard for $45
http://www.newegg.com/Product/Prod [...] 6813157315
4gb of ram( with Intel, speeds do not matter) $29
http://www.newegg.com/Product/Prod [...] 6820231253
Now, the key Item I would strongly suggest is a 120gb ssd:
http://www.newegg.com/Product/Prod [...] 6820147185
It will be about $100
A SSD makes everything you do feel much quicker. Even internet browsing has some I/o activity.
Have you considered a small form factor build?
You can build a ITX based pc that takes minimal room even on top of a desk.
The lian li PC-Q07 comes to mind.