Well, if it is the water temp sensor (green colour) which sends the info to the ECU and affects idle etc, then it costs around $50 from Toyota. I bought one less than 2 weeks ago from Castle Hill Toyota in Sydney. Just found the box it came from, but the part No is different from what you've quoted. Mine is 89442-20010. The water temp guage sender is located next to it under the coil pack, so you may be looking at the wrong one, or you could have a different motor from mine, which is an early 90s LS400 or Celsior.
Ric