I've heard others say they have gotten them for as low as $14.00 a key. unless you have the infrared remote key..
I plan on ordering a set of all new keys for my 1992 300CE.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.