Additional fee checkbox before and during checkout

I am looking for a order total mod where if my customers check a checkbox, it adds an additional fee to the total.

I want to offer my customers the choice of next day delivery on certain products.

Is there such an extension out there that I could modify to fit my needs?

This insurance extenssion is close: http://www.opencart.com/index.php?route ... 0insurance
But unfortunately it's not product-depended, and I don't want to buy it to modify it as I am not sure I'll succeed. So it'd be great if there's a free extension similiar to it that I can mess around with.

I found this great free extenssion: Charity Module http://www.opencart.com/index.php?route ... order=DESC

But unfortunately it's not for 1.5x

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

So you can just close the thread