Choosing the Hedging Method

Hi to you all,
I am using a combination of Open Tuition and BPP and have come across a question & subsequent solution that has thrown me (in BPP study text pages 390-391).

You are told that a UK firm has taken goods ($4m) and will need to pay in 3 months. All the Ex. & Int. Rates are supplied and the choice is between Fwd Ex. Market, Money Market or Lead Payments.

In both the Fwd & Money market choices Interest is considered however in the Lead Payment option it inst. The lead payment option suggests paying now would cost X and it takes the $4m using spot rate today. Inevitably of the 3 choices it becomes the least favourable.

My query is this.
Why in the solution for Lead Payment Choice does it not also add the opportunity cost (loss of Deposit interest over 3 months) to the overall £ value cost?

Thanks in advance….
Craig