How much to charge per email subscriber?

I'm working on a business model that helps businesses build email list subscribers. I'm working with local restaurants etc. I'm not sure how much to charge per email collected however. I have defaulted to €1 per subscriber for now.

What do you guys think? These emails would be quite valuable to these businesses, they can keep their name in their customers heads and retain much better customer retention this way and make more sales.

Any feedback will be greatly appreciated, thanks!

I don't mean to keep bumping the thread like this, I just want some opinions, this is the last bump. Thanks!