Purchased on craigslist for $1200 with a stuck shut hood and a purportedly blown head gasket. I replaced a broken coolant hose and have been driving it happily since.
Drivetrain Mods:
k&n cold air intake aka hot air intake
Suspension Mods:
M3 struts, springs, strut mounts, bilstein sport dampers
Wheels and Tires:
Z4 factory BBS wheels with cheap dunlop all season tires.