You know those ads that follow you around the internet? You visit a guitar site and then tons of unrelated sites suddenly show you ads for that guitar site? This is retargeting, where a site gives a list of users [1] to an ad network to try to bring them back in for a second look.

Normally you only get the "ads are following me!" effect when some company screws up by putting too much money into buying ads for too few users, but if you want to make your intended feel like you've bought out the whole internet to propose to them, that might be the effect you want.

By buying ads targeted only at their browser, you ought to be able to get this effect very cheaply. Perhaps they see 100 of these ads before noticing them, and it's a (very high) $50 CPM (cost-per-mille). Then you spend $5. Much cheaper than a blimp.

[1] The technical implementation is kind of roundabout: AwesomeCoolGuitars goes to MajorAdNetwork and sets up an 'audience', an advertising population. It starts off empty because AwesomeCoolGuitars has no way to tell MajorAdNetwork who belongs in it. So MajorAdNetwork gives them a bit of HTML to put on their site. That HTML loads something from MajorAdNetwork's server, and lets it set a cookie in your web browser. Later, when you load an ad on a different site that MajorAdNetwork does the ads for, your browser sends that same cookie back, which lets them know you're one of those people who saw whatever page you put the bit of HTML on.