Welcome to MrExcel!
I really wouldn't count on getting a job solely on the basis of your Excel knowledge. Most jobs where Excel is used extensively have a title like "Financial Analyst" where Excel is just a tool to accomplish a bigger purpose, not a purpose in and of itself. A big company which needs a process or system developed would likely use a more robust tool to do so, something specifically designed for the task, SQL, Java, or some other IDE. Smaller companies might indeed use Excel to develop processes, since it's easily available and the Swiss army knife of office tools. But they'd also have far fewer processes to build/improve. Once they had their processes working, they'd have no need to continue to change them.
This leaves contract work. And indeed, some people can make a living out of it. MrExcel has a staff of consultants who take on projects as needed. This would include these small business projects. There are some places on the web who hire people to do Excel piecework developing, but the returns are small. I looked into some of them, and concluded that I wouldn't get much more than pocket money out of it. If you set up your own company, it might work, but that's a fair amount of work, especially in building a reputation and drumming up business. Another route is by writing books about Excel or being a trainer, but that niche is pretty crowded.
I'm not trying to dissuade you from being a developer!! I've been one my whole career, and I've found it to be quite rewarding. But you need more tools in your tool box than just Excel. I've been a programmer, and there are many languages that are in high demand now, research that. If you're not into programming, IT encompasses more that that. DBAs, scripting, data architect, network admin, hardware engineer, testing specialist, the list goes on and on. Look around your country/locale and see what jobs are in demand, and find something that looks interesting.
Good luck!
