Got an HX too man...yeah, I've heard that the HX uses a special "wideband" o2 sensor, and yes, I'm pretty sure that is an accurate price. Though I think I've seen them online for around $250, though I would definitely make sure that those are the right ones, b/c companies sometimes dont know that the HX is different.

As for your fix, man I can't remember but that MIGHT be covered under Honda's emissions warranty...its 14 years or I think?? 150,000 miles. You say you have 155K, but if you documented it beforehand or find a cool dealer they might fix it for you since its so close to 150000...they get paid either way. I've had a problem w/ my EGR on my 96 forever, unfortunately I'm about 100K over the warranty.

good luck