On my engine, M103, the coolant drains from a petcock on the passenger's side bottom of the radiator with a male fitting that one may attach a 12mm ID hose to, and on the passenger's side of the block under the exhaust manifold (between #4 and #5?) there is a male fitting for a 14mm ID hose and a hex head (17mm?) to slacken/tighten - drain/seal the block. There is also an 8mm bolt on the driver's side near the water pump on the head that allows for air bleeding as you refill the reservoir.
Hope your engine is similar.
I think the best way to save some large $$ is to sometimes spend some small $$ . I'd buy the service manuals - on CD if available. You might start at http://www.mbca.org