How to sum two columns if one column might have two different variables which would call for a different calculation

I need to create a sum column (summing two columns), the issue I'm having is that the second column might have a result which needs to multiply the first column or it might have a result which needs to be added to the result in the first column.

Example

First Column (Estimated Costs)

50,000
100,000
5,000

Second Column (contingency amounts)

5%
10,000
10%
5,000

The first column will always have numbers. The second column will either have a percentage or an amount. I need to create a formula to sum either possibility. Is this possible or do I need to create two different sum columns for either scenario?

I tried using an OR statement with the SUM formula but it didn't seem to work.