If you're looking for a good forge lining, my first question has to be, where do you live? The reason this is important, is that if you live in GA or NC where they have an abundance of good red clay sticking out of the ground everywhere, all you need is a shovel and a couple of pickle buckets. Between my friends and I we must have built 5 or 6 forges back in the early and mid 80's. At least two of them are still running on a weekly basis.
It doesn't get any cheaper than this!