Special Values From Drop-down Menu & Total In Simple Form?

I have the perfect form for a client - but its missing one thing. She sells hair clips in various colors. A user can select a hair clip color and quantity quite easily (as seen in the code below). My issue is that she wants to be able to give the user a 'special price' based on the quantity ordered by the user. Contrary to simply adding the default price of $7 over and over again based on the quantity selected.The way I want it to work...

1 clip is $7
2 clips are $12
3 clips are $22
5 clips are....etc.

...however, with the way that the javascript is set up now I'm only able to select one default price. This means that whatever quantity is selected -- it's simply multiplied by the number 7 to provide a total.

1 clip is $7
2 clips are $14
3 clips are $21
5 clips are....etc.[code].....