Do you have Starwood points? You can transfer 20k of those to 25k M&M miles (you get a 5K bonus for transferring 20k).
You can top-up there cheaper than with M&M directly. They have a 20% off promo until the end of the year and with the current USD-EUR exchange it's even better than it was in the summer. 20k Starwood points cost 560USD with the promo. You can also expect 300-350EUR in taxes for the M&M award to the US.