You can get disc brakes from a 70-72 Chevelle / Olds for pretty cheap and they are a huge upgrade over drums. I’m going to do 4 wheel disc next year too. For now front disc and rear drum.
FatMat was a little over $100 to do more than the whole car.
http://www.fatmat.com/fatmat/bulk/100ft.htm
Call them and tell them that you wanted to get in on their $89 special bulk deal and they will probably drop the price for you.
They didn’t ship it to me in time to do my headliner 