Many writers do not consider all of the options available to authors and are often not prepared for the expense and effort required to go after this business. But one cannot start a fire without first investing in some wood!
One such possibility is public speaking outside of just book promotion. This requires research, planning, and the building of one's platform. Rather than discuss the intangibles, let me give everyone a rundown on some of the physical expenses and investment.
A professional website that focuses on speaking
A brochure that covers all speaking topics
Office supplies - paper, envelopes, postage, etc.
Investment in training and joining professional organizations
Travel expenses, such as gas and hotels
Willingness to make a lot of free appearances to build up the resume!
These items all cost money. Notice I did not even mention those things that will also cost time, such as researching and preparing subjects to discuss. But if you are not prepared, such expenses might sneak up and bite you in the butt! (Or worse, cause one to skip vital investments just to save money.)
When considering professional speaking, remember - it's an investment in YOU! It's also an investment into those who attend your events, depending on your subject matter. Be prepared for the cost of doing business.
And don't forget to enjoy the ride!