Optional Attribute with discount (depending on total order price)

[imoran]

I'm setting up a site selling promotional T-shirts.

 

I'd really like to do the following:

 

Depending what the customer wants printing on them, the customer can add an optional set-up (which is £35) and later depending on the total order, they can get a discount on this price (or even free). I'm guessing this is something that will have to be added after 'selected all their products?

 

Is there any way to do this please?

 

Iain.

[phrasespot]

You don't mention the version of you install, but if you are on 1.4, you could add a feature for the "optional setup" so you have the item with and w/o "optional setup", then in prices set a discount for the price limit you have in mind.