I'm adding RKE to a W124 with this kit I got on Ebay for about $45 depending on the exchange rate: eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices ignore the Honda in the title as it's a universal kit. I went with this one because the remote looks closest to the later factory remotes and it can use a switchblade key. The actual remotes that I got have the symbols on the buttons filled in with white so it looks even better than the picture. The blade key didn't match the key I had so I got a matching pair here for $10: BENZ KEY BLANK FOR FLIP/ FOLDING REMOTE MB48, W124, W126, W140, R107, R170, R129 | eBay The most expensive part was getting the keys cut. I called around and found one place that did it for $60 the pair. I haven’t installed the module yet, but already I like that I don't need to carry a separate remote and key like the other aftermaket systems.