Why not drive your M3?
I drive mine everyday. You could use that $10k on gas and other expenses or investments instead of on more insurance, tax, gas, etc...
Just my 2cents.
BUT if you do want to buy a gas saving DD, then you could always go for an elantra or civic?
2008 E90 M3
: Alpine White/ Fox Red Novillo
/ Brushed Aluminum
| Premium | Cold Weather | Technology | EPS | PDC | Ipod/USB
:: Adelei's Gas Mileage