Cheaper O2 sensor (archive)

Keep in mind that ALL (except some recent Toyotas using a type that works as a variable resistor) O2 sensors are a zirconium oxide semiconductor and all perform the same function, being to put out ~.5 volt at ~ .5% CO when at operating temp.
The only differences are:

Externally (wired) or internally grounded (to exhaust)

Heated or non-heated

With this in mind, you could wire a single wire Bosch or GM (used them when I did greymarket conversions) connected to the correct wire. A ground wire could be clamped to the sensor body. Heater leads could probably be ignored as their function is only to shorten the time before the sensor begins to read. (I don't know of any state that has a cold start emission test.) Just be sure to protect the hot lead from grounding out. Later OBD II cars can set a code for failed heater. In this case one might wire the old sensor to the heater in an out-of-the-way location or use a resistor (fairly high wattage rating) in the heater circuit.

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