We had a similar issue a couple of years back...
We had six workstations in the college's gym, one a register PC and five other staff workstations. The gym is on the other side of a small adopted road at the rear of the campus with an electrical supply independent of the colleges on-site substation.
At the time the workstations interconnected using a 3Com 4228G switch, in turn uplinking to the main campus network using SOHO D-Link wireless bridges and external high gain antennas. As time passed by we soon realised that the speed and reliability of the WiFi link (not to mention the potential security risks too!) was not suitable for carrying domain traffic. Also, having roaming profiles and folder redirection enabled didn't help with logon times for those using the gym workstations.
We ended up looking into throwing a Cat5e cable over from one building to the gym (attached to a tether cable) and we soon discovered the issues surrounding buildings with different power sources and the building regulations preventing this solution.
As mentioned by the peeps above the best solution would be to go fibre, that's exactly what we did and now the gym is uplinked at a healthy 1Gb/s to the campus backbone.
If I remember correctly the cost of the fibre installation didn't break the bank, the only real cost was that of the fibre modules for the switching kit.