Talk to amobia.co.za as far as i know they dont cover your area at all but the do private company solutions also and could advice further as to what you guys want to do.
I'm part of the ptawug and can tell you that what you want is very much achievable i dont think the LOS is much of an issue, it will be with conventional long range wifi equipemnt but using more expensive hardware and the NV2 protocol will allow for a good solution.
As i said get hold of them or search the forum/google for isp/wifi internet providers as most of them do pivate solutions
Good Luck
