By how much do the Thrifty Hacker and Vending Expert gene tonics lower vending machine prices, and how do they stack with each other?

Question

The Vending Expert gene tonic is described as "provides a slight reduction to prices in vending machines" while its upgrade, the Vending Expert 2 gene tonic is described as "provides a substantial reduction to prices in vending machines".

The Thrifty Hacker gene tonic's effects is described as "hacked vending prices are even cheaper".

By how much do the Vending Expert 1 or 2, and the Thrifty Hacker gene tonics lower vending machine prices? If a vending machine is hacked, how do the Vending Expert 1 or 2, and Thrifty Hacker stack with each other if both gene tonics are equipped?

Answer 1

Hacking a machine takes 20% off the price of most items.

Thrifty Hacker provides 10% off prices, but only when the machine is hacked.

Vending Expert provides 10% off hacked or unhacked prices.

Vending Expert 2 provides 15% off hacked or unhacked prices.

The effect of the tonics is additive with each other, but multiplicative with the discount provided by hacking.

To calculate the final cost of an item, use the following formulas.

Base_cost = Base cost of item.  This is the unhacked cost with no tonics.

Tonic_Discount = Sum of all discounts from tonics, per above
  up to (35%) for all three vending tonics

Hacking_Multiplier = 100 if the machine is unhacked.
                   = 80 if the machine is hacked.

Final_Cost = Base_cost * (Hacking_Multiplier / 100) * (100 - Tonic_Discount) / 100

The best possible price from a hacked vending machine with all three tonics is 52% of the base price of the item.

If you only splice one tonic, the best choice is Vending Expert 2, followed by Vending Expert. Thrifty Hacker is the least useful of the three, because while it provides exactly the same discount as Vending Expert, it only works on hacked machines.