TheoGrizz, I agree with your application of Jynn's ability and triggered effects, but your insurance example really is a terrible way to explain it better. Mostly because in real life, that invoice will likely show $3000 as the cost, with a $1000 deduction for the city law. So the argument with the insurance company would be that the invoice was for $3000, regardless of what the final cost charged was. The accounting in your example would result in either the opposite conclusion, or not resolve the argument at all.
Which maybe furthers the need for an official response to this. I'm not sure the RRG has a statement clearly saying at what point you check for a cost.