UPDATE: I Bought a used amp on ebay for $193 from partsconnectionnj. It arrived in about 4 days and was marked as coming from a 2008 Camry and was a 86280-0W390. I put it in this morning in about 30 minutes and the radio is working again.
This is a very easy repair that, contrary to Toyota's repair manual, can be done w/o removing the passenger seat. With the seat full forward there is ample room to remove and replace the amp. The hardest part was getting the plastic clips out to remove the cover. If you don't have a clip removal tool, you can use a screw driver to pry them up a little then use a needle-nose plier to get under each one and work it out. Then remove the bolt holding the ground wire and the bolt holding the amp to floor. Squeeze the middle of each of the three wire connectors and pull out. The wire harness is taped to a plastic strain-relief pin on the front bracket, which is a little hard to reach under the seat. It might be possible to pull the tape off, but I found it easier to break the strand of tape attached to the plastic.
The replacement came w/o the front and rear brackets which are held on with star-head screws (so you will need a set of star bits). It took about 5 minutes to remove the three screws from each bracket and reinstall them on the replacement amp. At this time I used a needle nose pliers to remove the strain relief part from the front bracket (once you have the amp out this instruction will be obvious). I did this to make it easier to rewrap the tape around it later.
Reinstalling took 5 minutes. First I reached under the seat, unwrapped a bit of the tape from the wire harness, and wrapped it back around the strain relief pin. Then I put the amp back in position, plugged in the three connectors, put the ground wire bolt back, and put the bolt back into the floor. I then turned on the radio and verified it worked again.
I moved the seat all the way back and from the front pushed the plastic strain relief part back into the front amp bracket. (Note: I'm sure it would be fine to ignore this tape and bracket connection and nothing bad will likely ever happen.) Then I moved the seat all the way forward again and put the plastic cover and pins back over the amp.
I saved at least a $1000 doing this myself (plus the inconvenience of leaving the car at Toyota). Even if this amp dies in a few years, I'd do it again and still save time and money.
I hope this info helps others interesting in doing this repair themselves.