hmmmmmmmmm............ why would you want these people to compete against you? you're already leasing it as a plugin. If they undercut you on price and are better positioned in terms of marketing to webmasters it's going to hurt your existing plugin business.
you should get a substantial amount if you're going to do it. Figure out what it would cost them to duplicate what you've got.
Why not just let these people sell it for a %.
email me
[email protected] and i'll give you my opinion on what it's worth.