You can get a used set on Ebay.  I saw a Telex set for $50 at the buyitnow price.
 
Don't get the David clarks H10-76 because the plug is different, it is for military airplanes and you will have to spend another $90 to get the conversion kit.  There are some David Clark's on ebay, but hahr to come by one under $100, more like $150 but still you can find a pair for around $100 if you really look hard.