I'm so sorry to hear about Noah.
This problem is very common with papillons and alot of small breed dogs. My vet said my papillon, Jasmine, was showing tiny signs of this at one of her check-ups when feeling around her knees, but that was normal. She said it's common and hers wasn't anything to worry about it, just could possibly cause some stiffness in her knees later on.
How old is he? Did your vet give Noah any medication? Poor guy!
My vet told me if Jasmine started showing any signs of pain in her knee, to start her on a glucosamine supplement. I don't know if that could be helpful at this point or maybe your vet went over it, but just wanted to suggest it. Is there a way they could work out a payment plan with you, so atleast you could get the X-ray done?
This site I found seemed to be about Boston Terrier's, but it explains all about what it is, and theres a link for a glucosamine supplement. That particular brand looks expensive, but I'm sure you could even get this at a vitamin store, I've seen it before there, actually talked to the guy about how he gives it to his own dog.
I hope he starts to make an improvement! Keep us posted!