One would expect that there should be a price matrix that might look like:

But if you only have simple products:

Black + 1″ = $1.00
Black + 3″ = $1.40
White + 1″ = $1.05
White + 2″ = $1.25
Chrome + 3″ = $1.55
Chrome + 4″ = $1.75

… then you don’t need the full matrix.  Even if you did need the full matrix, how do you set up simple/configurable product pricing in Magento?

Solution:

This Simple Configurable Products extension by Matt Dean.  From the extension page:

This extension changes the way that the pricing of configurable products works in Magento. With this extension enabled, a configurable product’s own price is never used. Instead, the price used is that of the appropriate associated simple product.

This gives site owners direct control to set the price of every configuration of a product, while still giving users the flexibility they usually get with configurable products. (There’s no more having to set rules such as: +20% for blue, -£10 for small, +15% for leather. You just price the underlying small-blue-leather product at £199.99 and that’s what the user pays.)

You still have to create the configurable products and set certain attributes to be the configurable ones ( e.g. “Color” and “Size” in the previous example ).  Set the prices of simple products (no need to set the price of configurable products), and the extension takes care of the rest.  In the front-end, users will still be specifying Color and Size, and prices will change accordingly.

Happy pricing!