Thanks! Yeah I did the same, editing each one in Districts to "NO_COST_PROGRESSION". This stopped the tech scaling, however I noticed that it no longer seems to scale with game speed (which I feel it should, I actually prefer marathon mode, makes the games feel much more epic). I left apostles in mine as well, though I did cut the increment in half-ish (from 10 to 4). I can kind of understand the reasoning behind settlers (so I left them as is), to make a progressive cost for each city you add, but not builders.
I shall try your mods as well and see if they work any better. Thanks waflmlk!
Edit---
I did notice that in mine I DIDN'T need to start a new game (although if I had begun a district it remained the same, but the rest were cut back down to 66 production cost).