+1 for the CPO option. I know a guy that had an Altima, and he liked it a lot. This is a guy that had previously driven a Lexus IS350. Not saying that an Altima is the same level of car, just saying that after driving the IS, being able to drive and Altima and not think "I hate this" is significant.
Also, according to him, keeping the Lexus in its warranty meant getting serviced at their locations, which grew expensive/
I would definitely say look for a 2 or 3 year used model. You won't notice much of a difference and you've let some other guy pay for depreciation. More importantly, you did say you were on a budget. Now, a 18K new Altima might be in your price range but a 15K CPO Altima would feel about the same, and I'm certain you could find a use for that 3K elsewhere.
Since you mentioned the Focus, that's another car very worth considering. The hatchback versions are pretty trendy with the college crowd right now. (Probably because of the low price, good mileage, and the fact that its small enough to park anywhere.) A Buddy of mine just bought a Focus titanium and he loves it. GO to a dealership, check one out, especially the SYNC/My Ford touch features and you might really jump on it.
This is one concept Ford really got figured out just right. Ford has cracked the code on the fact that people are starting to go after these small, economical cars with good mileage, SO, somebody realized, if you take a fairly reliable 12,000$ car, and pack it with another 800$ in gee whiz gadgets and tech, to the average driver, the perceived value just elevated by thousands. It really sets the cars apart. Consumers right now eat that tech stuff up. That's why the compact, budget Focus and Fiesta (a 13K flea speck of a car) can be ordered with GPS, Voice commands, Satellite radio, and push button start. All the sudden its "cool".
LIterally (I think they even said this in press releases) when they worked out the steering wheel buttons and LCDs (my buddy's focus has these customzable LCDs and touch screens instead of regular dials, gauges, and cabin controls) the designers were like "hmmmm what are our buyers most enamoured with right now? AHA! Lets make driving this car feel like using their Iphone."