The decision about how to acquire Microsoft licenses usually comes down to license terms and price. Here are some shortcuts to finding the relevant information on the Microsoft web site.
Open License Product Use Rights (PUR)
www.microsoft.com/licensing/about-licensing/product-licensing.aspx
Or create a customized document: pur.microsoft.com/products.aspx
OEM and Retail End-User License Agreements (EULAs)
Open License Price Spreadsheet
Search the web for “Open License Estimated Retail Price List”. The current URL is here:
At the moment, I am not able to download the spreadsheet if logged in as a Microsoft partner. However I can access it from an InPrivate session when not logged in.
Retail Pricing
I haven’t found a full price list, but you can always check www.microsoftstore.com.