Trying to convert result of formula to $ from HNL based on chose in validation column.

We receive payments in either USD or HNL. I want to be able to have a final price (last column) that puts all prices in USD. I have a reference cell on a separate worksheet (drop down inputs) that we will use to store the data for validations and the conversion rate. We use one conversion rate for all transactions for a fiscal year, so only need to update once a year. Not sure how to make this work.
Thanks,