I am currently studying for some Cisco networking certifications and have been thinking about this since the first email..
It just occurred to me that you could quite possibly run multiple (on different channels) wireless N point-to-point bridges and load balance between them. It would require a fair amount of initial equipment but because you wouldn't be renting any lines that's all you'd have to pay.. I have done some point-to-point wireless networking in the labs at RMIT but on older b/g equipment. For antennas you'd just run either a bunch of yagis or panels...