I voted $100, but that amount is easily higher. I figure the vet visit alone is gonna be around $50, just to see them, and then whatever meds are needed on top of that. But if the bill is around $200 and I can pay half of it up-front that day, most vets are gonna be ok working out a payment plan to finish paying it off the next month or two, and if that doesn't work, I can make up the rest on credit cards. So I don't necessarily have to have all the cash in hand that day.
From what I can tell, glider-knowledgeable vets know when anything is wrong with a glider, that time is of the essence. They want to treat the glider and worry about money later. And if you have a good relationship with your vet, I don't think it's that big of an issue either. They know you come in every 6 months and never have problems with payment before, much more likely to work with you than it being the first time they've seen the animal and it's 3am in the morning.