Upgrade Costs
Normal upgrade costs use base cost, cost growth, current level, and any room cost-reduction multiplier. New Game+ makes growth steeper.
For normal upgrades, each next level starts from the upgrade’s base cost and multiplies by its growth rate once per current level.
Room coupons reduce normal shop costs, but the five bodyguard bribes and five main coupon upgrades ignore that reduction.
In New Game+, the game increases each upgrade’s growth pressure by taking the extra growth above 1.0 and multiplying it by 1 + 0.25 x NG+. Bodyguard bribes instead cost one million times ten for each New Game+ layer.