Titania can be easily interchanged with zirconia, but you must make a small interface circuit that will essentially apply a gain of 5 to the voltage coming from a zirconia sensor (with roughly 0-1V output) to produce the 0-5V output typically expected by the titania-input ECU. The ECU is providing some small bias current (most probably way less than 10mA) to the titania input pin, but the amplifier circuit should have no problems with that. It actually works (I haven't permanently installed it yet -- have to make a nice wiring harness first) but is not very cost effective if you don't have the parts.

You need a small breadboard, some miscellaneous parts and relevant experience. As I believe a titania sensor could be had for about 95$, and a "universal" zirconia from FCP Groton goes for about $45, you'd need to fit your electronics in 50$ assuming you don't count your time.

Unless you're an electrical engineer or an electronician-hobbyist with most parts and experience at hand, it may be hard to squeeze the electronics in those $50. A decent enclosure (ABS at least) will cost around $10 itself, the breadboard goes for probably another $10, I doubt you can get a spool of decent (at least 120C/250F rated) hookup wire for less than $15 - that's 35 for the very basic stuff. The screw header blocks, the op-amp chip (needs to be rail-to-rail IO), the voltage regulator (even if just a zener diode), some overvoltage/overcurrent protection and other passives plus the shipping (around $7 for a small ground package from DigiKey) will easily add up to about $45. That's still assuming that you have a nice soldering iron and a decent flux-cored solder. You will also need small diameter solid conductor wirewrap-style wire to wire the breadboard itself. OTOH if you're into electronics, you'll probably have everything at hand maybe short of the enclosure.

So for me it was easy to do it, but it probably may not make too much sense financially for the typical brickboarder.

OTOH, once you do the electronics they will likely outlive the car so after initial cost you just change the cheaper O2 sensor :) So it may make sense if you plan on getting another 100k miles from the car at least.

It's also noteworthy that replacing zirconia with titania (don't know if it would make any sense though) would be even simpler, as all you essentially need is 4 resistors, a zener diode and a capacitor in order to reduce the voltage from the sensor and to provide the bias current. This stuff can be soldered together in-line and then just covered in shrinkwrap, no need for an enclosure nor a breadboard. I wouldn't suggest such assembly approach to the titania-to-zirconia interface which is more complex.

Cheers, Kuba