Buy this. Add About $3,000 for their warranty and you're covered on everything out to 125,000 miles for 5 years.
I'm tellin' ya, I spent the last two years of my life analyzing all this Z4 stuff. I went w/ a 3.0si just because I didn't want the maintenance costs. In the beginning I was M or nothing, but the more I looked at them and drove a few, I was open to a 3.0si. Plus mine was listed for $21,500 w/ only 23k miles on it. You might want to look at those too. It's really much more powerful than I expected. Of course, it's not M power, but I have no desire to track it, so around town there's plenty of grunt.
I even drove to Arkansas to pick up an M at a BMW dealer and walked away because it had a Vanos rattle.
http://www.carmax.com/enus/view-car/...results%20page