Well, its not an "extras" kind of thing. Heh. You have to order them, I am sure they will keep producing them after the group buy, but I highly doubt the RB-R will stay at the price of $750 shipped for us (us is defined as anyone who orders an RB-R through this thread in a reasonable time [probably ~3-4 months] after the information is announced). Just a warning for future buyers who stumble on this one in two years. If you order them outside of the 'HybridZ Group Buy', I would suspect he would charge more.
As for the tires. I wasn't planning on hosting a group buy for tires. So many people want different things. Also, tires ae pretty standard, a group buy on them probably wouldn't make much sense as it would most likely include a lot of logistics for little reduction in cost.