I got mine cheap on eBay because the seller did not mention RB1 in the title. Do a search for the different part numbers 56038629xx (with xx being AB to AI), this is how I found mine. Click on "Advanced Search" and be sure to check "Search Title and Description".
I paid only $465 including shipping for mine.
According to the Dodge documentation for the iPod kit, you want the AI or AH radio model if you ever plan on connecting your iPod. I have also heard of someone with an AD model radio who got the iPod kit working, but was never able to confirm. Oh, one more thing: The newest nav DVD will be released soon, so if you plan on upgrading to the latest maps, the release date of the DVD included with the RB1 you're buying should not matter much.
Good luck!