The lowest price I've ever seen on the SDS100 new is 649.00 USD. You might find a refurbished unit for slightly less. I'm sure there will be many folks coming on here with sites that have them for less, either as refurbished, or repacks, or factory repaired, etc. I understand some folks were about to save 50-100 USD going that route.
Check out my Radio Reference post in another thread that gives the full details of purchasing a brand-new SDS100 with a FREE Uniden A28100B nylon carrying case included for $650.00 or an SDS100 factory-refurbished by Uniden with a 90-day Uniden parts/labor warranty and two FREE Remtronix antennas included for $549.95: SDS100: - Any good deals out there on a new100?
They pop up on classifieds 2nd hand every so often, very rarely for under $600 though. Thing is you need to watch the new listings like a hawk and jump on it because they sell FAST!