I was able to build a new wireless bridge. I was given a Linksys WRT54G2 router that "didn't work". These don't have a setting to run in bridged mode, but the firmware can be replaced with the open source firmware from dd-wrt.com. (This firmware has far more features than the one that Cisco provides!)
Next I removed it from its shell and placed it in a surplus NEMA box. The antennas were simply hot-glued on to the circuit board. Working great!