Bootstrapping is the best way of running a small business on a low budget.
Here are some great ideas for keeping down your costs:
Specialisation: Your industry knowledge is very valuable and can earn you money. Share your wisdom online as much as possible (without giving away trade secrets, obviously). Contribute advice at online forums and start a blog.
Newsletter: Regular newsletters ensure that your business is kept at the front of the mind of your customers. An email newsletter costs very little to produce and is a great opportunity to up-sell or cross-sell various products to whoever is reading it.
Website: Remember to frequently update your website. This costs nothing and greatly improves your SEO. Try running promotions and competitions as this will allow you to build a list of people who are interested in your business.
Press Releases: The online press releases of today make it even easier for a small business to make announcements or promote products to a wide audience.