Is NGK 25002 only sensor I can use ??? It is kinda pricey.

Yup, you're now a 700 owner and that's the one used by the Siemens/Bendix Regina fuel system.

But they don't often go bad (thank Titania) and you can evaluate their function just like you could with the Bosch in your old 240 -- watch the voltage, once it is warmed up, idling. It should transition roughly between 0 and 1 volt indicating the ECU is responding to its output and correcting for it.

Of course, just like with the Bosch, absent this behavior doesn't mean the sensor is bad. A vacuum leak, faulty fuel pressure regulator, or leaking injector could put the car out of the narrow range in mixture meant to be controlled by the oxygen sensor. Read up on Rex/Regina in the 7/9 faqs.
--
Art Benstein near Baltimore

"I feel sorry for people who don't drink. When they wake up in the morning, that's as good as they're going to feel all day." -Frank Sinatra