Many of us use free blog themes, either out of the box, or with modifications. I use a combination of both free and premium, but nothing burns my butt more than finding a nice free theme, and not being able to get rid of the sponsored links in the footer.
Note : I do recommend keeping the links of the designers and sponsors somewhere on your blog just out of respect. I just blend them in with the blog roll, or at the bottom of my "About" page.
If you have ever had that problem, I found a nice little tutorial that will help you break through that mess of code.
How to remove encrypted footer links from Word Press Themes.