I have a very early pair of Time Windows. The value will depend on the condition of the drivers - they are a pain to get the cloth off and back on. You should be able to buy a perfect pair for $200-$300. I'm currently running them with 100wpc...but have used as little as 40wpc. I wouldn't worry too much about power, but anything less than 30wpc won't allow them to sing.
Larry
Larry