Blur, I have no idea about price speculation. If it really will be Scion and Subaru only in NA, expect Subaru to possibly cost a bit more than the Scion and the Scion to cost less. That might be offset by different features that will come stock on the Subaru. But at this point that is only guessing. Otherwise I don't see why Scion would sell for the same as the Subaru.
Just realize that donating (i.e. $2 like you mentioned) is not the same as becoming a member. In summary donating ≠ becoming a member. You will have to spend at least $20 for the intro level. I would just recommend going for the $35 and get the t-shirt in the process. If you really want the Subaru > Scion, spending $35 to save well over a $1000 seems well worth it. Just remember you have to wait 6 months before you can get the paper work to get the car. So say car goes on sale spring/early summer of 2012, you will need to plan your membership accordingly.