You have to find a way. There may be a chance that whatever is going on won't be as costly as your thinking but there aren't any details on that. If you have a regular vet that knows you they may be able to work something out with you. You can call around for low cost clinics. You can see if your local shelter has a lower cost clinic attached. You can see if there are any programs in your area that you may qualify for that help provide medical care. You can see if your history will go towards a friend or family member loaning you the money if they have it with collateral and a signed contract detailing payments you can and will make. Your last resort would be to check into surrendering your dog if you have no other way to attempt to provide necessary medical care. It is what we make the choice ot do when we choose to get a pet. We have to do what is best for them even when it may be the hardest thing for us.What you can't do is nothing and let them suffer by not providing a doctor's care. I'm sorry your pup isn't feeling well and hope things work out for you.
First of all..if you can't afford vet bills, perhaps you should not have a pet. They require medical care just like humans do and there are times when vet care is essential. Animals DO get sick, and it is your responsibility as a pet owner to see that they have proper medical care.