The reason why the newspaper upgrade ends up costing the most is because the prices for each upgrade rises exponentially.
Specifically, the rate of increase is approximately e^(n*C), where n is the number owned and C is the associated constant. Newspaper has the highest constant, and lemonade/oilfields have the lowest constant (lemonade will always be the cheapest to upgrade vs any other upgrade of the same level)
Biggest problem with the game: If you buy a high tier instrument, and then buy a lower tier instrument, you're stuck with the lower tier item with no way to equip the higher tier for the rest of the game.
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