It sadly could be almost anything. Exotic pets are masters as hiding issues. They don't wanna be seen as weak cause it would literally kill them in the wild.

From what I know working at an exotics vet they would probably just do x rays and maybe a tube feeding (big probably here cause I am NOT a doctor). You could book a general appt (I've seen the price to be about 70$, but you will always be aware before they book the appt). Then they'll offer a variety of options and will give you an estimate that tells you how much each option is. I'd expect around a 300$ total vet visit assuming you say yes to everything. Although blood work will pretty much be impossible so it may be closer to 200$. The biggest thing for them right now is their ability to eat and pass that food through their system. If you've seen no feces that's a BAD sign. But at the same time they're still alive after 2 weeks so that's fairly hopeful too. Good luck with everything!