Magento – magento : different shipping cost for some products

You can achieve this in 2 steps.

1.Create a discount rule for 50$ that applies only to your 2 products. Add the sku's of the products in the Actions tab under the section Apply the rule only to cart items matching the following conditions (leave blank for all items)

2.Create your shipping method and inside the collectRates you can access the quote items like this: $request->getAllItems(). See if both your items are in the quote and add an extra 5$ to the cost. if they are and the quote has your coupon code applied ($quote->getCouponCode()) then make the shipping 5$.
You can get the quote like this:

$items=$request->getAllItems();
$quote = null;
foreach ($items as $item){
    $quote = $item->getQuote();
    break;
}
if ($quote){....}

Or you can just create a discount rule for those 2 products for 45$ (50-5).
Or you can make your coupon enable free shipping and make the discount 45$.

By default that isn't possible, you must, at least implement:

• A custom Shipping Method
• A custom Shipping Form for your method, to allow customer select different shipping method for each item.
• Create sales_quote_item and sales_order_item attributes to save customer method selection

Your custom shipping method must handle all that logic, you need to split all items/weights and calculate the individual/total shipping cost/price and eventually some combination too ie:

- item 1 by usps = $10.
- item 2 by usps = $10.
- item 1 and 2 by usps = $15

Your shipping method must be able to:

• Obtain the shipping cost/price from the others shipping methods (for each single or combination possible item selection)
• Save customer shipping selection to sales_quote_item
• Recalculate all that data in all further steps in checkout
• Save quote_item data to order_item
• Re-implement any other -parent- shipping method feature, like Api calls for pickup, packages generation or tracking number getters

Finally if you want to give your customers a good communication feedback, you should modify all "post place order" email and templates in order to display all that information.

IMO is a lot of work to do, and I can't figure out a real-life case in which such effort would by justified.

EDIT

I'm not totally sure, but a partial use of some dropship extension may help... I guess