Shopping for lambda / O2 sensors - Part numbers and differences

Hi all,





I know there are plenty of threads on both front and back O2 sensors, and people have recommended Amazon for buying the NTK ones.





My question is this. Why are the RX8 ones so much more expensive than other cars? Even when you compare to other Mazda models or similar cars.





The fitting is generally the same (M18x1.5) and wiring seems to be a standard thing. So are there really differences between makes and model of sensor? And what are they?





As an example, looking at Denso sensors, what is to stop me using a sensor for an MX5 in my RX8?

UK prices (eBay, just for comparison)

Denso DOX-1449 (for RX8) - £150

Denso DOX-0317 (for MX5) - £85

Denso DOX-0323 (for MX5) - £110





All of these have the same fitting, and are front O2 sensors. What is the difference between these really?





The cynical side of me tends to think that it is too much of a coincidence that cars that are prone to emissions issues have more expensive sensors....





I would appreciate any info, or if I have missed an existing thread in my search, a link!





Thanks all