2006 Prius, Red Triangle came and went away

My 2006 Prius has been sluggish to accelerate lately. Today the red triangle popped up and it would no longer accelerate. Turned it off. A few minutes later it would run again but still had the triangle. Got it home. Let it sit for a few hours before turning it on again; this time no triangle but if I turn the air on the battery drains down to purple and the fan by the passenger seat starts blowing loudly. Took it to AutoZone to run the codes and all it reported back was that the car is "Emission Ready = NO". It is currently resting in the shade by my garage. What is the likely problem I'm dealing with here?

 

It's been quite a journey. My Prius had a P0A0F code and the dealership said the engine was shot and needed replaced for $8,000. I took it to an independent shop and they found the same code but didn't think the engine looked bad. They replaced the spark plugs and the misfires stopped. I drove it for 4 days before the red triangle came back with the same code. I took it back to the independent shop and they when through the diagnostic protocols for a P0A0F 238. Their end determination is that the transmission needs replaced. They also identified that it needs a dampner and cover assembly, which would make sense to address when you have the thing taken apart anyway. They found a used transmission with 98,000 miles on it that would come with a 12 month/12,000 mile warranty. The total cost would be $5,020.

I'm torn. They say there is no reason to think the engine won't keep going for years, it has 145,000 miles on it. That's a lot of money for a twenty year old car. However a used car to replace it will be at least $15,000 and have near 100,000 miles with no assurance it won't have issues in the coming years. My car had the brakes replaced 5 years ago and the power steering a year ago. I'm also thinking about the affordable taxes and insurance I currently have compared to something even 5 years newer.

What would you all do?