Since your skills lie in the field of web development, there is no better advertising venue for you than the Internet. Aside from buying ad space, there are a number of inexpensive ways to get your name out to the needy public.
1. Forums, Groups and Boards
More and more people are turning to freelance work and starting their own small businesses as a way to make a living. Most of them know they need a good website to make those businesses succeed. That is why you will see message boards, forums, and specified groups filled with people eager for information on how to procur a successful website. These are your potential clients. Make yourself a regular in these sites. Look for questions that your business could be the answer to. Don't spam, and don't be afraid to answer questions that don't point directly to your own business. Non-salesman answers will make you a more favorable and trusted contributor, and still bring your name and business into people's minds. To accomplish this, each answer you leave should be accompanied by a signature line that leads back to your website.
2. Become a Writer
Many business-themed websites are eager for quality content. Use your knowledge in the field to write and submit articles. Write how-to articles, reviews of new products or procedures, or explore the different ways the newest wave of designers are affecting the business. The potential topics are endless. You likely won't be able to expand on all the finer points of your own business, but you will be able to mention it in connection with the subject at hand. Most importantly, your author notes will be able to include a link to your website.
3. Find Some Fans on Facebook
The social networking site Facebook has taken the world by storm, with over 300,000,000 American users. Your business should have it's own Facebook page, and you should be a fan of it. Encourage clients, friends and family to also become fans of your business. Each one that does will be advertising the existence of your web development business to hundreds of more people, as well as inadvertently issuing a personal recommendation.
4. Pro-Bono work
Is there an up and coming business in your neighborhood that has no website, or a poor quality one? Do you know of any local charities or institutions that suffer the same affliction? Use your skill as a web designer to give these businesses and institutions a smart face to the online word. Doing it for less or even for nothing might come in handy as a write-off come tax time. Your only stipulation should be that your site design comes with a signature, and a link to your web development company on the front page. These websites will stand an samples of your work and will be seen and used by 1000's of potential clients.
Buying ads might still be an important part of advertising your freelance web development business, but they are not the only way. Sharing your knowledge and abilities can bring results just as surely as a freeway billboard, if you know where to direct your efforts.