i actually didn't play that long, I just found a really good strategy where I would upgrade mostly the amount of supplies I get and then once I could get like 300 supplies just on the first level i would go around the perimeter until I found the next stage, and travel the perimeter over and over until i got to a super far stage that gave me a ton of coins
the amount the prices go up does not correspond to the amount of gold you can get which meant it got to a point where i could raid like one city and have enough gold to buy like 20 upgrades