Ubercart pricing based on quantity in cart?

I sell products that are usually semi custom made.
I’d like to set up a webshop for these products and have tried doing it in ubercart because I already have an ubercart store.

As the products have a price component I’ll call order cost for now, which is only charged once for the total order, there is setup cost for the actual product and there is a price per item.

I would like to be able to create a product and enter the price for the setup cost and the price per item and then have the system calculate the price per item based on the number in the cart.

Example:

buy 1 of product with 50,– setupcost and 100.– per item is 150.–
But 2 is 50.– + 2x 100.– =125 per item
4 is 50.– plus4x 100.– = 112.50 per item.

Can this be achieved?
I now use attributes but have to enter ten prices per product but then customers can also add 4 sets of 1 to cart, which is too expensive, they should add 1 set of 4.

I hope this makes sense…!

Products can be seen here:
www.svendingtray.com/catalog

I have googled, binged and duckducked my head and fingers to a boil, for any and all open source cart solutions that could do this but I’m lost…

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