Next Day delivery - Additional shipping option

I have 3 current shipping methods:

- Pick up
- Private package
- Business package

Beneath these options, I'd like to have a checkbox for next day delivery with an additional cost of £30.

How would I go about that? I don't want to offer 6 different shipping methods like this:

- Pick up
- Pic up (Next Day Delivery)
- Private package
- Private package (Next Day Delivery)
- Business package
- Business package (Next Day Delivery)

I managed to modify the insurance extension to fit my needs perfectly.

So you can just close the thread