See main page for full description, but basic changes from v0.2 are:
(1) Set the increase per copy to 5/12 the original rather than adjusted cost, which means 25 hammers for most districts;
(2) Changed the special district discount to 1/3 instead of 1/2 so it's not quite as OP (for Germany in particular).
Main page has the updated list by district, and forum will have a post on my thought process.
District Cost Mod 3.00
Changes district cost to scale based on the number of identical districts already built