You just described the rotors I took off. When I tried to turn them they got too thin. Mercedes recommends that you replace and not turn them. Quality rotors on average cost about $ 50 to 75 installed. My rotors were also warped besides having the edges. Really can see the warp when you start to turn them on a lathe. Fronts tend wear faster then rears so you may get away with just fronts. Since I was doing the job I just replaced all 4 rotors and pads. Check Ebay for rotors.