Check your 12 volt battery
Did the dealer run a battery "load test" on the 12 volt? Just like a normal car the auxilary battery in a Prius will no longer hold enough charge after several years of use. I just replaced mine after 5 years since my car would not start if left sitting for more than 2 days. I found an excellent battery upgrade kit that is much less expensive than what the dealer wanted to charge me. You can order it at:
Disclaimer: I am not affiliated with this company. I am just a very satisfied customer. The shipping is very fast, I received it in 3 days with the standard shipping option.
That kit is for 2001-2003 Prius
Perelandra, I took a peek at that site you recommended, and it looks like the kit is meant to fit a Miata 12-volt battery into the 2001-2003 Prius only. If thoconfam bought the car in 2004, it seems likely that it is a 2004 Prius or second generation. If so, it would be good to compare the two 12-volt battery compartments before buying the kit.
2006 Prius Fails to Start
Lately my 6 month old Prius intermittently refuses to start. Press the Power button and the LED display comes up weakly and no reponse from the shifter. So, I hit the Power off and on a couple of times (a.k.a reboot) and it responds. This has happened 3 times in the last week. It's going in for service next week.