Finishing A Google Sheets Spreadsheet Calculator

I'm looking to create a google sheets-based calculator for the purpose of computing numerous factors from an online game that I play. The spreadsheet is 99% done, but I'm completely stuck on the last part. Essentially what the calculator does is compute the total cost and in-game "happiness" level based on which property and which individual property upgrades are chosen on a series of drop down menus. I would like to add an additional factor- two game "perks" that give either a 10 or 20% discount on an individual upgrade. However I cannot seem to be able to figure out how to incorporate the data from a second drop-down menu into the main cost column, in which each cell is linked to it's own drop-down menu. Here is the link to the spreadsheet if you want to take a look at it: [login to view URL] Essentially I want column H to automatically apply the "perks' if they are chosen by the dropdown menu, instead of having them as a separate column.