Long distance wireless?

I work in a school system; tight budget.
Hello all,
We have six schools and an admin building, all attached to our network through ATM service. We have one very small building (a shack) across the parking lot that has no wiring to it, aside from a phone line and electricity. Are there any wireless devices (Access points, antennas boosters, etc.)out there that would travel through a building and across a parking lot?

Thanks
GP