Yeah, WISPS are great aside from the high prices and slow speed. We have a few carriers around here, installation is generally around $150, plus $60/month for a 512/512 or $100 for a 3M/3M.
My $45/month cable modem for 15M/1M starts to sound pretty good after that.
I've looked at starting my own in another area a while ago but unfortunately the high equipment prices, insanely high bandwidth prices (which you usually need to buy from your competitors), and limitations of the equipment relative to going wired means that to stay afloat you really need to charge high prices like I mentioned for a relatively slim amount of bandwidth. I've also read stories where the plot goes something like "people want broadband, WISP sets up and prospers, cable company sees success of WISP, cable company sets up broadband for half the monthly rate, WISP dies". It's scary stuff considering how much the WISP equipment costs and how long it would take to actually payoff.
All in all, I don't see how a WISP can really survive against the traditional competition. Personally I'm a big fan of municipal fiber, but that's a rant for another day.