New HV Battery & inverter, still dies. Help!

I Purchased my 2001 Prius used in 2007, with 98,500 miles. On January 6, 2009 the check engine light came on. The nearest Toyota Dealer said we needed a new catalytic converter. They wanted $1500 for the repair. I purchased an after market one for $166 and had it welded in for $60, using procedures to protect the electrical system recommended from PriusChat. The muffler shop said my 12v battery was bad and the car would not start. (I discovered later that it was not bad, only discharged.) I used my trolling motor battery to drive home, and noticed the car was making a whining noise that increased as the power decreased. Prior to the car stopping altogether a fan type sound added to the whining. I could cut the car off for a short time, and it would start up and drive for about 10 miles before doing the same thing again. I drove it the 50 miles to the nearest dealer, stopping 5 times to cool off along the way.
They first did an "Induction system service" to remove carbon from the throttle body, for $52.87. This did not fix the problem. Then they determined I needed a new HV battery. We spent $2868 and had a new HV battery installed. I bought a new 12v battery from them for $146, which I installed myself. The car ran fine for 9 weeks, then the triangle of death came on again, and left my wife stranded on the side of the road, same symptoms as before, with the high pitch noise and loss of power.

We had the car towed to the dealership again, (Sunny King in Anniston Al.). This time they said the car needed a new inverter, which would cost $4008.41. I bought a used inverter off a wrecked gen 1 car with 70K miles and installed it today. (I have been a DYI and pro mechanic in the past, and actually enjoyed the installation.) I followed Toyota's instructions on installation, burped the inverter cooling system adequately, and fired it up. I still got the triangle of death, even after several attempts to disconnected the 12v battery for several minutes and start, stop and restart the car several times. After driving the car a few miles it again began to whine, fan sound, then lose power just as before.
I don't know if it was never the inverter all along, or the used inverter was bad. Maybe the HV battery they sold me was bad. Maybe they missed the diagnosis altogether, and the problem is in the drive train. I don't trust the mechanics at Sunny King, given they took about a week to diagnose the problem, admitting that they repeatedly had to call Japan for advice, and were puzzled by the codes. Initially upon unloading the car from the wrecker, they told me there were no codes flashing, and "it worked just fine". I insisted that they find the problem, given that my wife drives in dangerous neighborhoods as a social worker. It took them a week to make the diagnosis of needing a new inverter.
We are taking it to another dealership tomorrow to have the codes read again. What do you suggest? I have $15,000 in a 01 Prius that is worth $5-6K at best. (They offered me $100 trade-in as-is on a new Prius.) It has 139,500 miles now, so my 40,700 miles cost me 25 cents per mile, not counting gas, tires, and insurance. What recourse do I have? I would buy a code reader for this car if I could find one under $200. I am recovering from Leukemia, and I am exhausted and need to resolve this issue and get a dependable car. Should I just cut my losses and junk it, keep trying to fix it and drive it or sell it? I am stumped. Please help.