How the hell do I finish a run?

I get past the 4th area, kind of easily, but the 5th and the final boss is cancer. Guides recommend getting a +6 plate armor. How the fuck do I get through the game if I don't find it. What if I find it in the second or third area? There are not nearly enough scrolls of upgrade to get that high.

What am I supposed to do? I am missing something but I don't know what.