Buy half decent tires!
Having tires last an exceptionally long time isnt the necessary the best situation. Hard compound tires, or tires that get hard over time, takes away from the handling and joy of the M3.
AS 32Iscreamer said, it is a sport car. If you are planning to slap on some cheap all season tires, don't buy the M3...
I also agree with the Falcons. Not expensive and has good tires charactersitics in the sunshine and rain.
Now for the high flow cats....