You have to buy a quantity of 50. If that doesn't scare you away, then proceed. By the time you have them shipped to America, they'd be 500-600 each. Black market, so expect little to no support. At that price you get a dud or two it really cuts into your deal.
Parts-Express will sell you a quantity of four lms 5400 for $879 each through the request quantity quote. At that point this drivers value no longer is there when you consider the concerns.
The uxl-18 group buy for $410 was a much better deal by far. Also, the upcoming stereo integrity HST-18 driver expected to fall in the low $600 range should be a superior/safer purchase.
I talked with the op a bit about this and dropped the idea. Unless you went in person to verify the drivers and establish trust it's way too much risk to buy 50 and then hope they are all good and ship the heavy things all over the US to the group buy participants. Too many ways to fail. Now if one of these members in factories area wanted to sponsor the group buy and assure each shipping driver was good, maybe. Otherwise, stay away.
I'm currently waiting on my pre-order of four Ultimax 18" drivers due in Feb. I'm expecting them to be the new price/performance champion. But the SI HST-18 has me watching closely for updates on data-bass.com testing too.