Audiobook reward levels are in the works!
However, I don't believe that I can technically post them until the lowest audiobook stretch goal is reached.
The reason: The project has already reached its base funding level and then some, so the project will be going forward. BUT it is not guaranteed to reach that first audiobook stretch goal. If I posted backer rewards today that promised audiobooks, but the funding didn't reach that stretch goal to fund audiobook production, then I would have promised a reward that I could not produce.
When the first audiobook stretch goal is reached, and I add the backer rewards, I'll also add "add-ons" so that you can add a fixed amount to any reward level to get an audiobook. If you want to help the project get to audiobook level, you can choose any backer reward, and when the audiobook rewards are added you can either add an add-on for the audiobook or change rewards to choose one that includes an audiobook.
Sorry about the confusion--if audiobook had been part of the base goal then it could've been included in rewards from the beginning of the campaign, but with stretch goals I need to be careful that I'm not promising something I can't deliver.