Take a look at United's award chart here (note that prices are one way):
http://www.united.com/ual/asset/Unit...after_6_15.pdf
Realistically, in business (which is also F on two cabin domestic aircraft), you can get to Northern South America, Caribbean, Mexico, or USA/Canada (excluding Hawaii). Northern South America would require buying some miles but if you've got cash, buying 10,000 miles would be within your budget.
Buying revenue tickets and upgrading is kind of a sucker's game and I wouldn't do it. You'd be looking at a lot of cash+miles out of pocket.
Continental's website is a fairly comprehensive search engine for reward tickets to destinations in any of those zones.