Since the old car has 130K on it, I might as well replace the O2 senor. Where and how much should I expect?

 

Retail from Honda is over $200.

http://www.acuraautomotiveparts.net has them for a little over $164. Retail anywhere for the *actual* part is going to run you this much.

http://www.oxygensensors.com has them for much less. I've never bought from there though.

Your other option is to buy a used one... you could be getting one with 10k miles or 100k though. http://www.importautosalvage.com sold me a used one for $20. Their minimum order is $35 though.