As speed freaks, it is our nature to gravitate towards the most maniac version of whatever car we are looking for -- but for a few reasons you might be better served with the plain Jane version. First, you'll find that you are ability to mash the loud pedal in an M badged BMW is limited to a few stretches of cop-free highway, but get the base version of the same car and you can pretend you are Michael Schumacher on your local backroads with minimum fuss. Find this 2003 BMW Z4 here on eBay offered for $7,900 buy-it-now or make offer, located in Philadelphia, PA.
The thing you are looking at here was about the cheapest way to get into a Z4 back in 2003 -- with a base price around $34k, you didn't get much other than a simple 2.5 liter inline-6 and a manual gearbox...but, what you didn't get was excessive grip and the consequences that come with it.
The inline-6 under the hood had 189 horsepower and 181 ft-lbs of torque -- meaning 0-60mph took 6.7 seconds -- not a slow number, but not like the blistering 4ish seconds from the M version. Fuel economy will be decent (20 city, 28 highway) and the M54 is a basically good engine with cast iron cylinder liners in an alloy block.
Shod in 225mm wide tires on 17-inch wheels (all the way around) gives the base Z4 a great balance and the ability to have a little fun without becoming a triple-the-speed-limit menace like an M version. The best part of the el cheapo version is that you save quite a few grand on the asking price and more in insurance/maintenance/gas costs.
See a better way to drive slow and enjoy it? firstname.lastname@example.org