RAV4 died, Dealer says diagnosing will exceed $600

Long story as short as possible:

Mid July (7/14), my 2011 Toyota RAV4 battery lights, power steering lights, actually all lights were flashing as I was driving and the car lost power steering. and it wouldn't start. Replaced the battery and the car ran.

Wednesday, 9/4/24, battery light came on. Drove to the store and on my way home, all lights flashed as they did before and the car lost power steering and died. No lights would come on, it was completely dead. Towed to the dealer.

Dealer calls me today and said I'm $179 in so far for diagnostics. Tells me there's a lot of 3rd party wiring (remote start that had issues 4 years ago and the dealer disabled it) and until they fix/remove the 3rd party wiring, they cannot diagnose it. Until this incident, the car ran fine.

I asked if it was possible that the alternator went out and perhaps the car was eeking along the best it could with just the battery. Dealer said they couldn't tell me without doing all the labor to remedy the wiring and that's close to $600.

I believe the battery is dead and they haven't charged it. Granted, I'm not a mechanic, but wouldn't it be reasonable to try to charge the battery and then test it or test the alternator?

Hate to have it towed again to the shop I usually go to because it'll be another $200 or more but something doesn't seem to make sense.