Magento Connect: Simple Configurable Products Extension
In alpha, 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 child 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.)