Some people make the mistake of thinking that their logo mark IS their brand. Well, it's not. Your brand is your entire business and includes every touch point with your prospects and customers. I like to think of your logo mark as the face of your brand. If you market right, your logo mark will come to represent your brand and all it stands for. Consider logos like the Nike "Swoosh" or the Apple "Apple."
You see them and they paint a very clear picture in your mind of what these businesses' personalities are and what they represent.
Your logo should do the same for your business. Granted, you won't be investing millions of dollars to make your logo mark a household icon, but for your ideal clients, over time, your logo should come to represent your business, its personality and what it stands for.
For this reason, when it comes time to hire a logo mark designer, you need to make sure you hire someone who understands marketing and branding. They will ask you questions about your business, the personality you want to portray and what your positioning is. They use this information to develop a strategically sound logo mark to represent your business appropriately. If they don't understand this, they will design you a pretty picture. A pretty picture is not marketing.
One of my favorite, low-cost logo resources is Logoworks. For between $300-$600 you will get a variety of logos to choose from, and they do require you to submit a creative direction worksheet to ensure your logo correctly represents your business and positioning. Logoworks created my 10stepmarketing logo and my Twin Connections logo. And, they've successfully created logos for my clients, too.