Unless you buy solid aluminum stems, your installer should include stems, don't pay DT for them.
ER does not include any valve stems, and you can just remove them from the DT order. Tax, and EF are becasue they have a store in LV, so they have to charge NV fees.
So the result is $522 DT vs. $519 ER.
The DT advantage is that they come from NV, or Arizona instead of Florida.
Actually, the best deal right now is from Vulcan Tire.
www.vulcantire.com
They are a good shop that specialies in motorsports tires as well.
$112ea. + $46 shipping from Salt Lake, so $494 to your door and probably 1-2 days max shipping.