One thing that almost every landlord I have ever spoken to about this swears by is Craigslist. Although those of us who were old enough to remember certain horrific things that occurred in regards to that website may be leery, it seems like a good place for rental property owners to start. It is not only cheaper, but apparently much more effective to advertise on a website like Craigslist than it is to list your apartment in the local newspaper. This is because very few people read the paper anymore and it can reach tenants outside the immediate area, such as those looking to move for their jobs or trying to be closer (but not too close) to their families. Check out your local Craigslist listings and see if it may be a good fit for your property.
Another thing you can do is set up a social media account for your properties. If you post on Facebook about your apartments for rent, there is always a good chance that someone will happen to see them. In fact, many people look on social media for places to live as the interaction is instant and it is much easier to research the person you are talking to when it connects to their personal profile. There is a sense of security that people can get from looking on social media that may not extend through the more traditional routes.
Although it may seem a little odd to some of us, the internet is actually a wonderful tool for finding tenants and renters with little to no cost to you. Try it out and see if it works. After all, there's no harm in attempting something new.