You don't need Office. You can download
OpenOffice (for free) which does the same stuff. As far as AV -- yeah, you're going to want AV products but many major suppliers (Dell, Gateway, etc) provide you with AV for a cost -- usually around $90.
For $300 the salesperson oughta find you a good hooker.
I'd pay between $400 and $600 for a base-level computer (
probably even less) that is going to be used for mail, web, and word processing.
Cakes -- What's your thoughts on having a Computer/Video gaming-specific forum? Plenty of computer pros around these parts.