Facebook? Their business page digital marketing has a slew of options for you to spend $1 / day if you want - to target people searching for a similar product to what you are selling.
You can also use that ad to link to an interest form you can design, or a website, etc. etc.
You can target people in specific areas, say, people living in a rich neighborhood even. You can be so specific, and the person who's wall the ad is popping up on will have no idea you targeted their neighborhood lol.
Let's say a construction business needs to pull in a few more clients. They can throw out an ad on Facebook, (or individual contractors working on commission for sales who have developed their own business page,) targeting wives of guys who need something fixed, but aren't getting around to it. Set at "Female ages 25-45" and target a specific area. The ad can guide someone to your information where they can contact you.
Depending on the business, these types of things may need to be approved to make sure they are accurate, but if you're working with a business that has a little more freedom and doesn't have a lot of rules on wording, you may pull in quite a few.
It also gets your name out there.