Hotels may not have made inventory available on Priceline yet, since they expect that they'll sell more rooms in the coming weeks. DC hotels during the week can expect to sell lots of rooms to last-minute business travelers; the ~$100 rates that you've seen might have been weekends, or slow periods (i.e., when Congress is out of session).

The rates listed on Hotwire are usually a bit higher than what you can expect winning Priceline bids to be; for those dates, Hotwire hotels will cost $190-$260 a night.