I'm not sure whether you mean to make marathon not have units that are cheaper compared to the other difficulties, or whether you mean to make epic and marathon have units as cheap as normal, but if it is the latter, that is a big change in how the game will play out. AI with high probabilities for making units will crush any wonderspammer AI with ease, and you should be able to do the same. If you want everything to build faster, including buildings, this will also greatly alter the game, making everything a LOT faster (granaraies will be up faster > cities grow faster > build buildings even faster with more pop, including temples/happycap buildings which will let you have more pop> commerce/research buildings will be made faster > empire will find it easier to keep tech slider up > build more cities earlier > repeat > game over before the AD's). The thing I can't figure out for sure without playing is how slavery is affected. I think it will probably be weaker than ever (to the point of being weak instead of the strongest civic in the game), as what is the point of whipping a building that will be made in a couple of marathon turns? Also, the AI pay less in upkeep than the human for the same army, so that may play against you as well (but probably not). But either way, you shouldn't need a real mod, you should be able to just change some values in the xml file for the game. I am not at my regular computer, or I'd just give you the steps right here, but I'm sure somoene can help you find the directory/file and tell you what lines you wouyld have to change to make the game the way you want.