Call the guys at carsteering.com at (800) 399-7845.
They show the OE pump new at $385, and maybe by calling them you might get UPS surface free to Las vegas..they are good guys if you call..
New, njot rebuilt, no core return, then try eBaying your old pump, soemone might buy to rebuild or use as a core retrun...at leat some cash back in your pocket....
2003*Mercedes Benz*ML500*Steering Pump from Carsteering
I have used these guys several times on my other MB's, and they have always been straight..