Which car repair and maintenance cost more; 2008 m5 or merc e63

If you turn your own wrenches, it will be considerably less, no matter the vehicle. As for sourcing parts, I have used and know of MANY more BMW venues than Merc's. The folks at Daimler like to control EVERYTHING. That's my two cents worth.

if ur asking the cost of a service then u clearly need on you can afford to service these maybe out of ur bracket if u look at car like these then no matter what if u want then as service ost or running cost should not come into mind

Depends on what you break, if you have a good Independent shop in your city or if you DIY. Join the forums and do some research before you buy. Get a PPI before you commit to buying as well or you could be thousands in the hole for fixing inherited busted stuff!