the derailleur should run you 100-200 depending on condition, By the looks of things you should be looking for a 1st generation. You'll probably have to buy a complete set of front shifters.
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1 Super Record bike, 1 Nuovo Record bike, 1 Pista, 1 Road, 1 Cyclocross/Allrounder, 1 MTB, 1 Touring, 1 Fixed gear