1.5yo cat possible dental issues vet has no idea whats wrong

So a few weeks ago my cat Pixel slowly stopped wanting to eat, to the point where she became really dehydrated and lethargic.  I brought her into the vet and they checked her out gave fluids, did xrays found nothing. 

I brought her home she still didn't really want to eat, at this point she started to at least lick wet food but she didn't really want to eat it.  Even after being given an appetite stimulant.  So I took her back and they did blood work, and checked for a bunch of other things, everything came back negative. 

I brought her home again, still same issue she just didn't want to eat, so back to the vet I went for the 3rd time, where again they couldn't find anything wrong, this time they prescribed me critical care food from science diet where I was able to get her to eat some, but its still hit or miss, she only eats when she seems absolutely desperate for food, but she ate more than she has before.  However she still isn't willing to eat, but screams for food and runs to the kitchen for food, but just won't eat when i put it in front of her.

So I watched her eating carefully when I gave her some dry treats which she loves but wouldn't eat, sometimes she would try to chew them but leave a bunch of crumbs and other times she would pick them up and just drop the food out of her mouth and never chew it up.

My assumption is there is something going on with her mouth but when the Vet does a quick check they see nothing so I wanted them to do a sedated check, but at this point one of the doctors is just determined to run ultrasounds and test all her insides out which I CAN'T AFFORD.  I have already dropped $700 on tests and they have found nothing and I have no money for this.

I'm at my wits end 4 appointments later and now she just wants to refer me to get more tests when all i want them to do is an oral exam while she is sedated, but at this point they have sucked me dry leaving me with no money for the tests that probably need done.

Guess this is more of a rant than anything at this point but any one have an ideas of what would cause this or similar issues?  I have seen her drink a little but I am making her drink a few ML of water/pedialite via syringe a few times a day to keep her hydrated if I can but i'm starting to lose hope that I'll ever figure this out before she just fades away into bones.

While it is true that it could be dental issues it could also be nausea.  My IBD kitty had his first flare at 18 months and he would do the same thing with food.  He would pick up something and chew and chew on it then let it drop out of his mouth or let it drop back out without chewing.  The think with a kitty this young it could also be foreign body ingestion.  The vet was sure it was a foreign body with my  kitties first flare.  He was hospitalized with multiple xrays.  Gas patterns that don't change is indicative of a foreign body.  Patches went several days with no changes then he came out of it.  In his case it was more along the lines of his digestive system having shut down because of the IBD.

Given his age if he doesn't have the raw red gums that come with stomatitis which is very easily seen I don't think dental issues would be to the point of not eating at all.  I know that diagnostics for this stuff are very expensive but I have spent less on an ultrasound then a dental.  If there is any  way you can swing an ultrasound I think that would be a better way to go then the anesthetic for a dental exam.  

Thank you so much for the tip, I'm going to have the vet they referred me to do an ultrasound as well to check her out.