My cat Duncan (a wee bit over a month shy of being 19), has renal problems. (I say "renal problems" because last it was actually given a name, which was over 2 years ago, the ER vet referred to it as pre-renal disease. His last several bloodtests have shown that his BUN and CREA levels to be considerably lower than when he was diagnosed, and were even within the normal range, so I don't know what stage it would technically be considered at this point.)
He is on Phenobarbital for epilepsy, KD soft and hard food, Felovite 2 vitamins, water through the mouth via syringe, and Enulose (spelling?) which is for his hard stools. He recently had 2 Enemas for severe constipation (both given within 24 hours since he was very badly clogged since his body had sucked all the water out of his poo causing him to get backed up), Baytil (given for a few days after the enema), and Laxatone (laxative.) The enemas were given I think about 15 days ago, (sorry, very sleep deprived right now, hard to think straight.). After returning from the enemas, he seemed very weak and wasn't eating much, so after 2 or 3 days I started blending the KD canned with water and feeding him via syringe (by mouth) since he already willingly takes his water that way. For several days he seemed to plump up and looked stronger. He hadn't pooed in over a week since the day he returned from the enema, so last Saturday we took him back in to the vet. He felt his insides and said that there was nothing in there. I asked why and he said that was because of the liquid diet, nothing to worry about.
Thursday he did a small pee in the morning. He seemed like he wanted to do more, but nothing came out. Later in the afternoon he felt very light, and was rather "floppy", not walking, and out of it. The vet was gone for the day, but the nurse was still there and said she could check him out and give him fluids. She gave him sub-cutanous fluids, and said he likely only had hours to live. After a few hours of "convincing" I finally got mom to take him to the pet hospital, where we were charged $115 to be told that the bare minimum they recommended would be stay overnight with IV fluids for over $1000. They ideally wanted him to stay 3+ days. Unfortunately, this was way beyond what I could spend so we took him back home.
He managed to make it through the night. Our vet was called at his other office (he has two branches), and the situation was explained, and we asked if he could do an IV fluid. He said to stop by our normal office (which doesn't have hours on Friday.) at 2:45 PM and he'd check him out. He said his heart was beating strong and healthy, he was so dehydrated that his body sucked up the pee out of his bladder, and was even sucking the water out of the muscles in his legs, then he gave him another sub-cutanous fluids, and a shot (can't remember it's name, but he said that's supposed to kick-start his motabolysm [spelling?]), and to come back in tomorrow at 11am. With any luck the shot will have helped him become stronger, and he'd give him some more. If now, he'd have bloodwork done to see if there's any other options that could give him more time with a good quality of life. If not...well...I'd rather not go into that...
Is there any thing you guys can suggest that would help him live longer and have a good quality of life, or should I just enjoy what's likely my last few hours with him?

[Why must this happen so close to my birthday?

]