I think a lot of the posts I've read are overly optimistic about the cost of the M3. The base price may very well be $35k but options will add up quickly and option cost will be fairly consistent with the MS. That said, there will probably be less customization and more option packages to streamline the manufacturing process. I'm expecting that over time there will be more features included in the option packages with no price increase and option packages will be consolidated. This will be a subtle way of dropping the price people pay after the tax credit expires (so demand doesn't drop off a cliff) without upsetting those who ordered early on and paid more. Also, keep in mind the base model likely won't even be available for at least a year after the initial launch (supposedly in 2017), and probably not until after the tax credit has expired. Signature orders by early reservation holders will still cost 70k+, even into the $80s fully loaded, before tax credit.
That said, here's my guess at to what an M3 option list might look like at launch (if such a detailed option list actually existed):
Base 35k
50 kwh battery inc. (200 mile range)
$10k - 65 kwh (250 mile range)
$10 - 80 kwh (290 mile range)
$2k - Supercharging (inc. with batteries larger than 50 kwh)
$5k - AWD
$2.5k - AutoPilot
$3k - Tech Package
$2.5k - Air suspension
$2.5k - Upgraded Sound System
$1k - Cold weather pkg
$1k - Paint (anything other than black or white)
$1.5k - Sun roof
$2.5k - upgraded Wheels
$2k - leather interior
$2.5k - upgraded leather
$1k - Upgraded interior pkg
For me, I think I'd at least want to have the 65kwh battery ($10k), Autopilot ($2.5k), leather ($2k), and the tech package ($3k) for a total just over $52.5k. Getting a M3 80P (P not available with 65) will be $70k+, not in the 60s.