I was told by vet that my 12 yr old German Shep has a quarter sized m in his rectum. (prob cancer)?

As long as he is comfortable, he can be probably be sustained without surgery while you acquire the means to get him the surgery [however long it takes and if you still feel it is completely necessary]. I personally would not wait too long to get him the help he may very well need. Just do the best you can [and it sounds like you are].