Base reward per wave
Base_Reward = 15 * wave_number.
Effective wave yield
Current_Wave_Yield = Base_Reward * (1.0 + 0.2 * multiplier_level) * (1.0 + cloud_farm_bonus + weapon_bonus).
Upgrade cost scaling
Next_Upgrade_Cost = 500 * POWER(1.18, current_multiplier_level).
Path A (direct save)
Waves_Path_A = (Target_Expansion_Cost - Current_Cash) / Current_Wave_Yield.
Path B (upgrade then save)
Waves_Path_B = waves_to_buy_upgrade + waves_to_save_post_upgrade.