There are some options out there, other than giving the dog up to your local animal control or whatever.
First of all Care Credit, which is a credit card that you can only use in Vet offices, plus I believe doctor and dentists as well. It's an okay way to pay the vet for now if you don't have the cash up front. Usually they give you something like 6 months interest free. You make monthly payments until the balance is paid off the same way you would with any other credit card.
If that doesn't work, try doing a google search for IMOM, or look into other organizations that help. Some of them are strict about who they accept but they help pay vet bills in emergency situations.
Talk to the vet about organizing a payment plan. If there are any shelters or low cost vet clinics in your area you should talk to them, they may be more willling to work with you to keep costs down and may be more willing to accept payment plans.
Worst case senerio if the dog is suffering and you cannot find the money, you should be able to surrender him to animal control. If he's a pure rotty maybe try looking for rotty rescues, they may be more willing to work towards getting him better than your average animal control shelter would be.