Its really not as expensive as you think though... I would do some research into good techs to properly diagnose and do the repairs for an estimate before trying to tackle a conversion. I do agree that the power issue is a good one.
In no means am I against it, I just think that the prices you seem to think everything is aren't really as high as you think they are.
Do some checking through fastlane or partsshop here on this site. I am sure you will find parts to be pretty well priced.
And checkt he good mb shops section for a recommendation of a good shop near you to have the car estimated at. It wouldn't hurt any to get a few extra prices.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.