I'd think that the 04' RS's would be pulling a bit of a premium due to the feature set. I know I'd have traded my loaded 03 for one given the chance before it was modded.
The cheapest you can get would be one that's been crashed and rebuilt or driven hard and put away wet with latent defects or poorly chosen modifications. I've seen them for well under 20K. But, let me give you some advice as you've had experience with DSM's as Warrtalon and I have. Don't cheap out on these things like the DSMs. You'll cost yourself a lot more in the long run.