That certainly sounds like the sort of activity those active on social sites would be participating in. Facebook for one has their own advertising system with great demographic targeting based on user profile data, besides targeting for example unmarried women between 18 and 30, living in the UK, you may be able to identify employees of certain major companies or special interests mentioned on their page, the ad system gives you an estimate of the number of matches a given setting provides. While sponsored search keyword ads target people on an information seeking mission, you are interrupting someone's social meanderings on Facebook, it may be better for first contact recruitment of people who don't yet know they need to have a trip
CPV (Cost Per View, aka PPV) ads can be quite inexpensive, they reach a portion of internet users who have signed up for certain toolbars or game packages that include voluntarily installed adware that cause popup window ads to appear in their browser a few time each day. You can target any web site or individual page of your choice with a popup window ad.
Some CPV nets
TrafficVance $1000 minimum deposit (Advertising professional referral required)
MediaTraffic $100 minimum deposit - complicated, quality fizzled
Lead Impact $200 minimum deposit #2 Good place to start
DirectCPV $100 minimum deposit Brazilian, Latin American traffic
Adoori $100 minimum deposit