$172.50 US + shipping on Amazon :
$117.94 + free shipping ( maybe not to Canada ) on fleaBay :
Secondary Emission Control Smog Air Pump fits for Mercedes Benz 0001403785 | eBay
tons listed in Canada all the way down to $54.99 Canadian on car-part.com ( look under 2004 Mercedes SLK, then choose 'air pump', then SLK320 )