If they both already have Internet access you can get a couple of inexpensive LinkSys office routers like the RV042 which will allow you to create a VPN tunnel between the two offices (this works no matter how far away the offices are from each other). If not, and you have line of sight between them (and roof access) then you can get some WiFi equiptment and some high gain antennas and use WiFi between them. It won't be rocket fast, but it should get the job done. Anything else like Microwave or laser will be pretty expensive.

If they both already have Internet access you can get a couple of inexpensive LinkSys office routers like the RV042 which will allow you to create a VPN tunnel between the two offices (this works no matter how far away the offices are from each other). If not, and you have line of sight between them (and roof access) then you can get some WiFi equiptment and some high gain antennas and use WiFi between them. It won't be rocket fast, but it should get the job done. Anything else like Microwave or laser will be pretty expensive.