I'm not certain this is true. And targeted advertising certainly makes it less true, not more. Advertisers are not excluding low-income users from advertising, instead they're targeting more products at them that those users are more likely to buy.

Untargeted ads for higher-cost luxury products might make the Internet cheaper for low-income users, but that's not what is happening in the ad industry right now. Ads exist to get you to spend money, and they are just as targeted at poor people as they are at rich people.

I wouldn't be that surprised if the effect is the opposite, since poor people have less access to research resources, comparison shops, and trials that would allow them to combat the psychological effects of advertising. They're also generally under a lot more stress and time-pressure when they shop than rich people are, which is likely to make them even more vulnerable to manipulation during a difficult purchase decision.