Is Nintex Workflow supported on the Free SharePoint Edition?

if you mean SP Foundation then yes.

reg. pricing, I affraid you will not get an answer here

Pricing is based on the amount of workflows you require, and the features you're looking for. Ie, if you want Workflow, or Workflow and Doc Gen and Hawkeye...

Well, that's the subscription model, but there is the unlimted license which is based on WFE's as well. I'd contact Nintex for details as I doubt Nintex and their clients will want to disclose individual agreements between organisations.

I just talked with Ryan Orehek today from Nintex. He's given me all the details.