Woo Themes has some nice free ones; this one comes to mind: https://www.woothemes.com/products/swatch/.

A license for something like Canvas can be between $50 and $100 depending on whether they have a sale on.

You may also consider a theme from Theme Forest ($25-$45). Just choose something with a lot of sales and recent activity in the support threads.
I have personal experience with several of the themes with the most sales. I have found the MySiteMyWay.com themes the easiest to learn and use:

WordPress - Awake - Powerful Professional WordPress Theme | ThemeForest

WordPress - inFocus - Powerful Professional WordPress Theme | ThemeForest

In the end, you want to purchase a theme from a company with a long record of great support.

I have personal experience with these:

woothemes.com
studiopress.com - Genesis Framework by StudioPress alone or also purchase a child theme.

They're pretty easy to use.

I've used elegantthemes.com. They're inexpensive and have some decent themes, but when I last used them (about 2 years ago) I didn't find them very customizable, which is why I stopped using them.

I do not have any experience with Inkthemes.com but they seem to have some nice looking ones. I can't speak to how easy they are to use, though: InkThemes: 40 Easy Responsive Premium WordPress Themes

In sum,

For ease of use, flexibility and professionalism, I would recommend StudioPress.com and WooThemes.com.

Woo has a lower cost of entry, but Studio Press offers the best value if you know you'll be sticking with their themes for a long time.

Hope that helps a bit.