Business owners today are lucky to live in the golden age of self-promotion. Thanks to Twitter and Facebook and a dozen other social media tools, publicizing a company has never been easier or more affordable. As long as you have a computer and a decent grasp of language, you can probably do a pretty good impersonation of a public relations professional.

But public relations – the real stuff – is about more than likes and retweets. And nearly every serious small-business owner will eventually come to realize that to really grow a business, you need the help of a professional.

“All businesses need to publicize and market what they’re doing,” says Eric Tyson, author of Small Business for Dummies. “The question is when does it make sense and when can you afford to hire somebody to do it.”

First, some things you can do yourself: Establish a social media presence and keep it lively (solicit feedback, run contests, send exclusive coupons to followers). You can also probably pitch local media on your own. “A lot of town papers are always looking for editorial content they don’t have to pay for,” says Tyson. Consider writing a column that relates to your business without overtly trying to sell anything. “As long as you don’t send them something super promotional, they’ll be wiling to run it.”

But for the bigger stuff (national media, press conferences, large-scale promotions), you should partner with a professional. And that’s going to cost you. A large PR agency can easily charge business clients $20,000 a month. On the other hand, it’s not hard to find a good freelancer who’ll work for $50 an hour. This is just one reason it’s important to shop around.