Buy a domain name, hire a web host, install and configure the software from wordpress.ORG on that host, export your content from here and import it into the new self-hosted blog. http://en.support.wordpress.com/moving-a-blog/#moving-to-wordpress-org
You will be responsible for all installations, all upgrades, all troubleshooting. If something goes wrong, you have to figure it out and fix it. Be careful about where you get themes and plugins. Some of them are written very badly and have security holes that can compromise your blog - some of that sort of thing is done on purpose. Some even have malware built right into them. Caveat emptor - let the buyer beware.
Figure an average total cost, including the domain name, of $10 to $25 per month average depending on bandwidth and storage costs (stay far away from "free hosting - you get what you pay for). If your blog here is established and has page rank with the search engines you will be starting over from scratch with zero (0) ranking and you will have to rebuild that page rank. Figure about a year for that to happen - or more.
Be aware that you will very likely NOT make big bucks advertising, because for most bloggers, that simply doesn't happen. Most make $100 or less per year, especially with the downturn in advertising and lower rates the ad networks are paying now. Some make enough for a couple designer coffees and a scones per month after subtracting their domain and hosting costs. Unless you are getting over 10,000 hits per month, figure your revenues will likely only cover your hosting costs. Part of it of course depend on the nature of your content. Some types of people are more likely to click on ads than others.
Another thing to keep in mind is that the public is becoming very tired of being bombarded by ads, and ad-blocking add-ons for browsers, such as adblockplus, are zooming in popularity. Adblockplus has been downloaded more than 53 million times. I have them installed on both of the browsers I use and I will never see ads. If I do, I just zap them and then never see them again.