My Prius only has 32,000 km so I haven't had any out-of-warranty experiences although I have heard of other's issues. I think the biggest thing working against you here is the age and mileage of your car. The mileage is "up there", 148,000 km and the car is 6 years old, long beyond the standard warranty period. If you had an extended warranty that may help but I suspect that given the age/mileage they will not do much (if any) goodwill. I have heard of cases of Toyota covering like 1/2 the bill, but that's in cases where a person is just beyond the warranty period.
You are on the right track though, if you're not happy with the dealer's response then escalate. Keep it up until you talk to someone higher up the food chain

Good luck and keep us posted.
I too am waiting for a plug-in hybrid Prius (PHEV) version before I buy another one. The 2010 is nice but there's not enough "new" stuff to make it worthwhile to spend the cash on the newer vehicle. Too bad the Lexus "version" of the Prius only gets 50 mpg (Imp) as I was thinking of upgrading to it. What would you rather take? 71mpg with a current Prius or 50 mpg with a "better" Lexus? Easy decision...