Would a legitimate journal send unsolicited email to an author offering to feature an article in their own publication, for a fee?
Absolutely not.

While open-source journals can charge authors to help recoup the publishing costs in the absence of paid subscriptions, it is completely dishonest for a journal to "republish" a work that has already appeared in print. It is even more dishonest for them to charge you to do it. At best this is just an advertising service; at worst it's a scam.

I wouldn't even dignify the email with a response. Send that email into your junk folder.