If you are looking for great free and affordable WordPress themes I can highly recommend WooThemes (affiliate link). Their themes are really professional, clean and they have hundreds of them. Most are paid but there are some great free ones and the paid plan is very affordable.
I’ve used them for a lot of my own secondary sites including this one (BizzNizz theme customised a little bit).
Here is a sample of their free and paid themes, check them out.
Free themes from 
Bueno
Irresistible
Meta-morphosis
Skeptical
Snapshot
Rockstar
Premium
Here is a sample of some premium WooThemes. These themes are available to anyone who purchases our starter package.
Empire
Therapy
Cushy Theme
Editorial
Retreat
MyStream
