I don't have one, but I've watched Taig CNC mills on ebay for years. New they're a little more than your budget ($2500), but used they're sometimes pretty low priced.
They're really small, essentially a jewelry mill, but most stuff on a robot isn't so big.
You'll need the right computer to go with and software and tooling, but I'd consider this.
You can also buy the mill with manual cranks then upgrade to CNC later, to spread the budget out.
http://www.taigtools.com/cmill.html
http://www.ebay.com/sch/i.html?_from...+mill&_sacat=0