Wingnut's vet bills

Three days ago our boy-cat, Wingnut (full name Professor Wingnut-Whatnot) suddenly fell ill. Most of the day he was his happy-go-lucky self...playing "I'm not touching you!" with the dog, jumping the fence with ease, teasing his sister and auntie cats...and then in the late evening Edwin found him. He was so lethargic, he was almost completely unresponsive. He felt hot, his eyes were drooping closed, he didn't move or purr when petted, and when he did try to walk he was obviously in pain, and he strained several times, unsuccessfully, to throw up. We sat with him, talking to him and petting him, reassuring him he'd be fine. Occasionally he would seem to perk up, which kept us thinking he was feeling better, and thus kept us from off rushing to the Emergency Vet. Edwin slept downstairs in the basement with him, to be close to the litter box just in case, and kept an eye on him until morning, hoping we'd see an improvement. We did not. 
Off to the Vet: Trip 1
9am Saturday morning, Edwin took Wingnut to the vet. They were obviously very concerned and ran numerous tests: iStat Chem8+ Panel, PCV/TP, Urinalysis, physical exam. Nothing. Everything came back fine. They gave him subcutaneous fluids and an injection for nausea, and $325 later, they sent him home. 
And so we waited. And we tried to give him water with a syringe. He swallowed little dribbles, but still wouldn't eat. He wasn't pooping more than tiny amounts, and wasn't peeing at all. And we waited and hoped...
Off to the Vet: Trip 2
Today he went back to the vet. They ran blood tests again. Nothing. They took x-rays, concerned he may have eaten something that was causing a blockage. Nothing. Another $550, and still no answers. And, because he's now completely dehydrated, hasn't eaten or drunk, pooped or peed in three days, they kept him there. He's now hooked up to an IV, and will be there until at least tomorrow. As of an hour ago, they called and said there had been no improvement. The overnight stay and intrevenous fluids are essential, but also they are going to run us way more than we can afford. We will easily top $1000 by this time tomorrow. If he's still not better and has to stay longer...well...I just don't know what we'll do. We talked about it and decided that we just had to ask for help for Wingnut. We don't want to have to bring him home without a diagnosis. But we can't afford what we've already racked up, let alone what is coming. He's a sweet, wonderful kitty, the youngest and kindest, most playful and loving of our three kitties, and we don't want to lose him. Please help us if you can. Anything at all will be greatly appreciated.