The folks over at PhoneArena put together a handy little comparison chart for the Samsung Galaxy S4 on the primary four U.S. carriers, Verizon, Sprint, AT&T and T-Mobile. As you can see they shared known availability dates, pricing as well as a total cost of ownership comparison. For the most part it appears that VZW (once you factor in the $200-250 price of the device) is the most expensive total cost of ownership, with AT&T in second, Sprint in third and T-Mobile is the cheapest.
PhoneArena also included four of the secondary carriers like Cricket and U.S. Cellular, Ting and C Spire. If you want to see a comparison of those, hit up the source link below, but not much is known at this time for most of them.
Source: PhoneArena