For a minimal fee, players can export most Rock Band 2 songs to the third game.
Harmonix's John Drake confirms that Rock Band 3 will allow players to export songs from Rock Band 2 for a fee, similar to how Rock Band 2 allowed song export from Rock Band. The feature will work for all three console versions. Pricing and details have yet to be announced, but as before some songs may not be exportable due to licensing issues.
In addition to this, Drake explains that while regular songs will be priced at $2, content made for Rock Band 3's Pro Mode will probably be more expensive due to the songs featuring a lot more elements the team had to work on.