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camera, flash, the two lenses you have, and a good backpack was a total of $600, 2 or 3 years ago. I've seen the 30D advertised for $200. The 30D is reputed to be a significant step up from the 20D.
same sensor, but a bigger screen, ability to do 1/3 stops, and larger buffer? As far as upgrades between models go, I wouldn't call it significant. used 20d goes for $150 or thereabouts nowadays, so I guess the price difference isn't that big anyway though.