need advice on a networking device

I've got a simple network in ONE building. The people there need to access a server in anOTHER building a few city blocks away.

Someone set up a wireless link that joins the buildings, and it works. The people CAN access the server as needed.

What doesn't work is the person who set it up made the gateway in the OTHER building the gateway for the ONE building, resulting in the ONE building basically merged with the OTHER building, using their internet and DHCP and so on. This is undesirable.

I know that I need to set up a route in the ONE building so that only requests for the server use the bridge. Hook the bridge up to one particular LAN port, set the route to that port.

Any recommendations on a low cost business wifi router that will accomplish this task simply and properly?