So-called private sales are gaining popularity among discount e-tailers. Travel search engine Kayak is getting in on the action with a service that aims to make hunting for hotel bargains easier. Members who sign up for a free Kayak account can choose to receive an e-mail every Thursday advertising limited-availability offers negotiated with the site's most-searched-for hotels. One recent sale, for instance, featured deluxe rooms at the swank Snake River Lodge & Spa in Teton Village, Wyoming, for $165 per night, reduced from $275. Users can click on a link in the e-mail and reserve rooms right on Kayak's site. The private sale service will be integrated into Kayak's mobile app this summer.