I'd say low $xxx for it if someone has a good idea on how to use it. It's not that good to have the word "free" in a domain name if you want to make money from it. But it could be used as a reqruiter for a paid SEO service to get more sales. So, in the end it's all up to how far people want to take it. It would be great if the domain already had a lot of backlinks to increase the value.
Thanks for the appraise, yes planning to add some free important seo related plugins for the users to check their site ranking compared to their competitor.