here's how you get a good detector for $150.... Save the extra $60 and get an Ace 250 for $210.
Unless you find a used one (which many people shy away from), you're not going to find a good detector for under $200 bucks. Don't waste your time with a radio shack special. If you do, you'll either end up 1. hating the hobby, and sticking your $150 detector in the closet (waste of money), or 2. realize that the detector isn't cutting it, and end up spending another $250 for the Ace anyway.
Steve