How to stop cells displaying results outside required parameters

Hi,

I need to find a formula that can stop a value being returned once certain peramiters are exceeded.

For eaxmple, a policy is valid for 7 days.
The start date is January 4th, and expiration is Kanuary 10th.

I need to display the number of days used, and the pro rata cost of the policy used.

The problem is regarding policies which start before the required start date resulting in an overstatement in policy value, and days used. (highlighted in red).

Ideally, I need to somehow fix the values returned in the red cells to the total cost of the policy. ie, it has been used, therefore 7 days cost applied, and not eight, and £70 displayed instead of £80.

I hope my explination is clear enough. I have attached a sample data.

Thanks all in advance

Sai