BleepingComputer.com: Connecting Two Trailers Wirelessly

I am trying to ad users to an existing network that is at a construction site. We have 3 trailers on site, about 25 users, a SBS 2003 server, and a router. The router, server and about 7 users are all in one trailer. Then we have a cat 5 cable running to another trailer that is directly beside that one with a switch connected to it and about 10 users in that trailer.

Now the problem is that the third trailer is across the parking lot, about 75 to 100 feet away from the trailer with the router and server in it. That trailer has about 7 or 8 users in it and they all need access to the server. We can't run a cable to that trailer so we need to get the signal across the parking lot wirelessly.

Another potential problem is that this construction site is in a power plant and there are high voltage lines running over head of the 3 trailers. I don't currently see a problem with interference inside of the trailers as far as a wireless signal goes but I just wanted to put that fact out in case it is a problem.

Can anyone give me some good ideas of what type hardware I should be looking at to do this with and what I will need to know to do the set up.

Thanks for the help as always.

Lenny