I bought the M-techs from Maximillian's, www.bimmer.com
I believe they were on the order of $349 shipped for a set of 4. They were special ordered & had to come from Germany & took nearly a month to get here but worth the wait. I'm sure BMA could order them if you had a specific BMW part number, maybe someone who has them can supply that info. My local dealer can't even decipher the ETK spring tables but Maximillian's is very familiar with them, just tell him what factory equipment your car has -- a/c, etc. since there are a bezillian different springs depending on weight.
The Vogtland deal sounds pretty good. I would have tried them if I knew about them at the time. Dinan's are good also but around $400 for a set & I don't think he sells just the fronts. Maximillian's will let you order individually, but best to do all 4. The BavAutos were too soft & sagged over time. It lowered it 1.75" in front initially & kept dropping. Looked great but rode for crap. Two years later it had dropped 2-3/8" & bottomed out all the time. Suspension is one area best left up to the Bavarian engineers, it gets expensive to do it trial & error, not to mention repeated labor. If I put Koni's up front, it will be the 3rd time I'll have messed with it in less than 15k miles.