You are correct it is "a".
Reason was simple.
Customer was under duress and needed to get a job done. You stated a price and they accepted that price. That agreement was important.
With "b" - "whatever it costs is ok!" they could come back and say "Wow I didn't know it would be that much". So even though most people would go for "b" my experience was "a" was better.
Of course now if I wanted to argue the other side I could say if you really were trying to jack up the price than "b" might be better. Why? Because you are jacking up the price so if the customer say "I didn't know it would be so much!" you have some flexibility to throw them a bone and lower the price and make them happy.
My attorney on bills typically puts in all the hours he spends as "time spent, time billed" giving you some idea that you are actually saving money. As if he is cutting you a break.
"and future endeavors"
Right because you managed expectations successfully. Same reason perhaps paying $35 for parking is not the same as getting a $35 parking ticket.