OTOH, a used 5D classic (Mark I) can be found in exactly your budget range: (
KEH listing).
Everybody else has listed the advantages the 60D has over the 600D, but I should perhaps point out that they share the same processor and sensor. So it's all usability features the 60D has over the 600D. ISO performance, video capability, and overall image quality however, will remain the same.
And there's the fact that if you can hold on for three or four more months, the fall announcements are due to start happening in September/Oct. And the T4i is rumored to be on deck. Generally speaking, announcements happen in the spring and fall. So, April and October are probably the best times to go new camera shopping to know you aren't going to be superseded any time soon.
And since you're in the USA, I would also mention
Canon's Refurbished store. And
the Canon Loyalty Program. I got both my 50D and 5DMkII on the CLP. The 50D's MSRP at the time I got it was about $1200. I got it from the CLP for about $700. The 5DMkII was about $2500 at the time, I got it for $1800. Both of them had shutter actuation counts under 100 when I checked them, which means they were likely units that simply could not be sold as new, not repaired units, but that is a chance you take with Canon's refurbs. They only have a 90-day warranty, not a 1 year warranty, and come in a white box not a retail one. But they have been thoroughly checked by Canon Service, not something new cameras coming off the line can claim. I've owned the 50D for nearly three years, the 5D MkII for 18 months. Both are still going strong.
Right now, on the CLP, a 60D body is going for $640 + sales tax, and a T3i for $480+tax, if you have an out-of-warranty Canon camera to trade in. Just a thought.