What is your networking knowledge and ability like?  Do you understand wireless frequencies, channel width, channel separation, site surveys, Fresnel zones, etc.?  Who is going to provide you a re-sellable internet connection?

What you are wanting to do is not impossible.  If you understand the above principals its not really difficult but it does take time to set it up.  Do you know why the current providers have difficulty?  Is your terrain such that it is difficult to get a clear line of site between radios?  Are they using radios or configuring them so they can't support the desired data rates?

I have setup numerous wireless links.  In the beginning is discounted the difficulty of what I was doing and tried to cut corners.  I've still got one location that is giving me issues and will probably require me to replace a handful of radios and relocate one at my expense because I didn't do my homework in the beginning.  Fortunately the customer is being patient.  All my links are after the ISP provided internet connection and involve connecting farm buildings and yards.