This is a pretty good package price with free shipping :

Mercedes Benz Serpentine Belt Kit - E320BELTKIT | FCP Euro

 

Great find, buddy!

 

They also supply a limited lifetime warranty, however if you DIY , it's gonna cost you 10% extra :

1.Product must be purchased from FCP Groton.
2.Product must be registered on warranty.fcpgroton.com within 30 days of installation.
3.Product must be installed by an ASE certified technician. If the product is not installed by an ASE certified technician, FCP Groton does not provide a FREE limited lifetime warranty. FCP Groton does however provide the option of purchasing a limited lifetime warranty for non ASE certified individuals who plan to install the product themselves. The cost to purchase a limited lifetime warranty is 10% of the cost of the product. To purchase a limited lifetime warranty, please email warranty@fcpgroton.com
4.Product cannot be modified

 

That is cool! Kind of sucks that you have to pay extra for DIY though...