Your ad competes with lots of other ads and its placement for visibility is dependent on many factors that are outside your control. Unless, you add some bold lettering and similar features, it probably won't stand out. Price a weekend ad with no fanfare print or pictures in a printed medium within a major city. In just one or more weeks, you will have paid far more than an Internet ad for a full year. Unlike a paper, the Internet is also international and has many visitors that are not located in the United States.
Most Internet users are relatively affluent.
When you use a fully marketed Internet ad you get to market to more people than you could dream of reaching in most classified ads in newspapers, magazines, and similar media. Not only that, most of these people are prequalified. That is, they usually ran a search engine to find such ads, or information that makes it probable that they would like to check it out. It's easy to see that you could wipe out your investment value with such ads. Since your ad would be here, the overall marketing of the website will attract people to it.