Yes, most abscesses are fairly easy to deal with, with antibiotics. Do take kitty in. I've dealt with more than I can count...and I can count the ones that needed medication on a few hands only (well, it was ALOT of cats!!! :) )
An infection on the head if not treated can be VERY serious, if it spreads, for obvious reasons.
He needs to be taken to the vet NOW, just because your last cat needed many trips to the vet doesn't mean this cat will, his immune system is probably already low due to his age, pets can be a 20 year responsibility so please dont give up on him now for the sake of a few dollars and because he's 17, he could still have a few good years left in him. Ask the vet if you can pay by installments if it becomes expensive, I'm sure you could come to some arrangement.
I wish I could give you the answer that you're looking for, but unfortunately I can't. It's important to have this abcess looked at by a vet, ESPECIALLY because of the age of the cat. A bad infection in a cat his age could be very dangerous, so it's very important to make sure that the wound is lanced and cleaned and at least an antibiotic salve is put on it.
Ghilly