Keep your eye on Ebay for a used MB set.

I have found one source for legal W126 re-prints, and they are selling you the CD + contracting to print one hard copy for you, S&H may be extra..
IMO: it is cheaper to buy the CD and print it yourself..

Mercedes-Benz 280 S, 280 SE, 300 SD, 450 SE, 450 SEL 1973-1980 Repair Manual
$47.00
http://www.mercedesmanuals.com/Mercedes_Benz_W_116_Shop_Manual_p/w116.htm

Mercedes W126 Chassis Print on Demand Paper Manual
$379.00
http://www.mercedesmanuals.com/Mercedes_W126_Chassis_Print_on_Demand_Paper_Manual_p/w126print.htm

TOTAL = $426.00