Marketing is hard. A lot of people say that they do it, but usually it is either thousands of dollars, or it isn't done very well. When I started my company, I had a mission to fill that gap as well that I could. I am finding what I could have told myself from the beginning: there is a reason that nobody else is competing with me in this space.
Marketing on a shoe string budget can be difficult, but not impossible. The key with any successful marketing campaign is to be creative, and then make sure to measure results. The biggest thing that I see with a lot of established marketing firms is complacency. They create a campaign and it works, so they don't change anything from it. What if that campaign could continue to work better? How can we improve upon that campaign?
Art is creative and impossible to accurately measure, and marketing can be that way. What is the actual value of a specific tag line or logo? You can't put a dollar amount directly to it, but you know that it has an impact.
Science is very measurable. You can test and re-test and see similar results. Many advertising campaigns can be that way when you run a similar creative in a similar fashion, you will likely get the same results.
The difference comes in, well..... the differences. What is the difference in running the same ad in two different magazines, or on a Tuesday versus a Wednesday.
For small businesses, you want to make sure that you do your best to understand the measurable and testable part of your marketing plans. Keep as much science backing up what you run as you can, but don't leave the creative spark out of your planning.