Total Cost Event with Cost Term calculated as a formula

Hi all,

I'm trying to construct an event where we will use Total Cost.

We have one item on lot level. We ask the supplier to provide an amount - "Purchase_Price".

In addition we have a few internal variables:

Resell_value_%

Interest_rate

Discount_period

I'm able to calculate a formula that uses:

('Total_Cost'*'Resell_value_%')*((1+'Interest_rate')^-'Discount_period')

The result = Resell_value

But how do I get the Total Cost calculation to include the result of the formula I created?

Or how can create a Term that automatically will be updated with the formula I have created? And then have that Term included in the total cost?

Any suggestions are warmly welcome.

Chr