So, not quite your dreams, yet - but getting closer for 599. this is what you get. We got this off the Apple Store website just now. This is brand new and RAM and hard drive are cheap to upgrade. I'm sure you could get a new, previous-generation with a little slower processor for the price you're looking for. Check Ebay, Mac Mall or the Apple Store and look for 'open box/refurb/clearance' sections.
MAC MINI
2.0GHz Intel Core 2 Duo
1GB 1066MHz DDR3 SDRAM - 1x1GB
120GB Serial ATA Drive
SuperDrive 8x (DVD±R DL/DVD±RW/CD-RW)