Hello,
I apologize for the delay. This case is likely too complicated and difficult to provide much assistance via text.
In all of these cases I think it is best to contact as many local rescues and pet care providers as possible. This might mean reaching out to your local shelter and veterinary college. You can also start a go fund me page. Post on all social media accounts and personal accounts. Start with general practice vet who the rescues recommend. Give them a realistic budget for you. Ask about payment plans and payment plan companies like care credit or vetbilling.com. There are places to help. Keep trying and keep asking.
Hello,
I think that there are really only two good options. See if you can find another general practitioner to review your pup with an examination and a review of what you have done already or take the referral for the best chance at getting your diagnosis.
In some cases your original vet can call for a consultation with the veterinarians who provide the diagnostics. You can ask about this. It is free and often gives them access to a specialist without the cost.