Magento – Magento showing Price Difference in configurable Products

Here is how you can get the prices of the simple products. The example is for a single configurable product but you can integrate it in your loop.
There may be a problem with performance because there are a lot of foreach loops but at least you have a place to start. You can optimize later.

//the configurable product id
$productId = 126; 
//load the product - this may not be needed if you get the product from a collection with the prices loaded.
$product = Mage::getModel('catalog/product')->load($productId); 
//get all configurable attributes
$attributes = $product->getTypeInstance(true)->getConfigurableAttributes($product);
//array to keep the price differences for each attribute value
$pricesByAttributeValues = array();
//base price of the configurable product 
$basePrice = $product->getFinalPrice();
//loop through the attributes and get the price adjustments specified in the configurable product admin page
foreach ($attributes as $attribute){
    $prices = $attribute->getPrices();
    foreach ($prices as $price){
        if ($price['is_percent']){ //if the price is specified in percents
            $pricesByAttributeValues[$price['value_index']] = (float)$price['pricing_value'] * $basePrice / 100;
        }
        else { //if the price is absolute value
            $pricesByAttributeValues[$price['value_index']] = (float)$price['pricing_value'];
        }
    }
}

//get all simple products
$simple = $product->getTypeInstance()->getUsedProducts();
//loop through the products
foreach ($simple as $sProduct){
    $totalPrice = $basePrice;
    //loop through the configurable attributes
    foreach ($attributes as $attribute){
        //get the value for a specific attribute for a simple product
        $value = $sProduct->getData($attribute->getProductAttribute()->getAttributeCode());
        //add the price adjustment to the total price of the simple product
        if (isset($pricesByAttributeValues[$value])){
            $totalPrice += $pricesByAttributeValues[$value];
        }
    }
    //in $totalPrice you should have now the price of the simple product
    //do what you want/need with it
}

The code above was tested on CE-1.7.0.2 with the Magento sample data for 1.6.0.0.
I tested on the product Zolof The Rock And Roll Destroyer: LOL Cat T-shirt and it seams to work. I get as results the same prices as I see in the frontend after configuring the product by Size and Color

Welcome to the wonderful world of configurable product pricing.

If you don't want to install an extension you need to set the configurable product to the price of the base item (75cm @ $2400) and the price of the 85cm option to $73 fixed, which will make it always more $73 more expensive than the 75cm one (and will display (+$73) in the option dropdown with the default theme.

Assuming the simple products are not in the catalog or searchable, the price you set for them is irrelevant.

As Reinsch has said, there are extensions around that will try and work in an easier to use format.