Fix or Sell??

Well this mechanic that you trust that charged you $800 for 2 oxygen sensors.....you might want to not trust him so much. It took him maybe 15 minutes to remove and install the 2 sensors. Those sensors online cost maybe $100 each on the average......so you have to decide how trustworthy this person is.

The p0420 is almost always a catalytic converter problem. You can buy the part on Amazon for $100 and have a muffler place weld it on. That would be all that's needed to fix your problem. Here's what you want to buy on Amazon. It's the Catalytic converter that's closest to the engine that needs to be replaced......there's 2 of them.

Magnaflow 99205HM Universal Catalytic Converter

 

I just bought an '07 with 185K on it, so I wouldn't think about walking away...

Anyway, you need a new mechanic. First step is to replace the aft sensor for about $100 installed and monitor its behavior. If it mellows out, good. If not, 99% chance you need a new cat. He overcharged the crap out of you because he thinks you're a sucker.

A bolt-on Magnaflow 23007 is only $300.

 

I think the cat is easier to replace than both the o2 sensors

Kenny

 

I have to agree.
I would have "reservations" about a mechanic that charged me $800 for sensor replacement.

 

Welcome to PriusChat! I wouldn't take it personally; unfortunately this is not atypical. Knowledge is a good thing, so asking questions and getting information is the way to go. You still need to find someone to do the work (unless you learn to do it yourself) so an informed conversation with your mechanic is a place to start.

 

This MagnaFlow unit requires no cutting or welding? That sounds terrific if that is the case. Thanks.

 

California requires carb compliant cats, which only the dealer sells.

Other states can use the aftermarket stuff

I personally don't like aftermarket bolt on exhaust hardware, they rust much faster than oem

 

If you place a nice ad on craigslist as a "for sale or trade", someone will probably trade you a nice 350z or maybe a firebird and you can give your money to the gas station instead of a crooked mechanic.

 

2008 and 186K.

Well, baring the post about just buying a high mileage car above I would have sold before starting these repairs.

Many are saying your mechanic is over changing you.
I don't know you area labor rate or the Toyota list price for the sensors...so gather that info..maybe he is not overcharging. My area labor hourly rate is $150 sometimes even more.

So based on the comments "I can't really afford a new car", watching insurance costs, make my opinion/ vote to repair.

2008 means some warranties until 2018....maybe look at the other threads with high mileage Prius' and check your warranty book.
Bumper; forget about the repair as long as all the lights are functioning and aimed.
Cat Convertor, you could install an aftermarket and still pass smog testing (brand will not be checked during testing... only exhaust output and OBD checked), yet OEM always fits well and should have a long life. Risk of aftermarket failure and re-install labors within 2 years is possible additional cost.
Tires and brakes OK?
Seems to me $2000 of repairs is less than one year car payments, new DMV rate and new insurance rates.

So just some rambling comments from me.

Good luck in your decision.