"the vet quoted me a price of $1800 (yes, $1800) for Norman's treatment; this includes what he has already done in an attempt to cure the cat without surgery, the surgery itself, and care after the surgery."
I don't know how much of the $1,800 you've already incurred, so I'm not sure how much the additional surgery and follow up would cost.
But I would definitely spend the $. I have two cats that are older (17 yrs. and 14 yrs.). They basically still act like kittens at times (being very playful), and are extremely affectionate. They act as a welcoming committee to anyone who comes over to visit us. Cats live a long time; much longer than dogs, it seems, so hopefully the $ will be well spent for Norman to be a healthy pet and companion for many years.
You sound very attached to Norman and hopefully you'll make up the $1,800 soon. I will certainly keep you both in my prayers!
And certainly heed the advice of the other FReepers to get a second opinion. Maybe another vet could provide either different and/or cheaper methods of treatment.