Keep an eye on Ebay, I think there is one there right now for $80 and it comes with the cruise amp and the SRS voltage capacitor and the panel they mount on. They pop up often on ebay and you can use one from a diff model car like a W124. Good luck, they are stupid expensive even at online shops.
Good luck

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red