Look for one of the little Radio Shack stores that will close at the end of this month. Today they are giving 20% off all sales of remaining stock. Since the Wistler is $200 - $100 on sale you get another $20 off for a net cost of a mere $80 for a nice little portable RD.
I bought one and I like it so much I plan to keep it. If someone breaks into the car and steals it I haven't lost anything compared to a detector that cost four or five times as much.