My dog has an abscess on his face and I don't know what to do?

My dog has an abscess on his face, i first noticed it 1 and a half- 2 years ago and it has been steadily getting bigger. In the last couple of months it has doubled in size (now about the size of a golf ball) and blood and puss is coming out of it. We took him to the vets a few weeks ago and they suggested a few options: Sticking a needle in to take a biopsy and make a decision from then, or operating. The biopsy would be �100 and the operation around �500 in total. We decided not to go for the operation as he is 15 and healthy otherwise, but it has been getting worse and worse despite us cleaning it with antiseptic daily. He won't wear a dog cone and he keeps rubbing the abscess and making it worse. Please help!