Starting an online business is not FREE, regardless of what some internet marketers would have you believe. However, compared to a brick and morter business, an online business is relatively cheap to start and maintain. There are basically two types of expenses: recurring expenses and one-time expenses.
One-time expenses will be for hardware such as a computer (although I seem to go through one every two years or so), computer add-ons such as a printer, external backup drives, office furniture and software that you use on a daily basis.
Recurring expenses include those that you have to pay for many times (monthly) during the course of a year such as advertising expenses, autoresponder services, business license (if required), domain name registration, DSL or Cable, and office supplies.
Your domain name must be registered every year and you can usually get better pricing if you register for two or more years at a time. Register your domain name through a service like GoDaddy that provides a backend administrator to easily manage all of your domain names.
You may be required to obtain a business license for starting and maintaining an online business in your City. Check with your City to determine what your specific requirements are.
There are optional expenses that can make your online business run more smoothly that you may want to consider as well. For instance, one software package that I find indespensible is the Affiliate Organizer to keep all of my affiliate information in one place. Another service you might find useful to subscribe to is WordTracker to keep in touch with the latest keywords entered into the search engines by people looking for your services. Another great piece of software to use for researching Google Adwords, cost per click and keywords is Keyword Elite . Also consider a billing service if you are sending bills to clients. I currently use FreshBooks , and as far as online billing services go, it is the best there is, and it will make your business look and feel professional to your customers.
The bottom line is that you can run a "no frills" online service or you can add a lot of "bells and whistles", but don't forget to plan for the necessary expenses you will incur.