Depends by the track in question. To resell it the way you say means to give up the artist name on it as well, which goes even beyond freelance exclusive licensing. For an average long track and below average effort put into it we’d charge no less than 3000$ for considering doing something like that, and we’d have to absolutely NOT feel emotionally attached to the track (it’s your own work after all).
If the production on the track is stellar to our standards and lenght is average, I believe we’d have to talk no less than 10000$ to give it up 100%.
Because a track is not profitable until now, it doesn’t mean tomorrow you won’t get the deal of your life out of it. You have to believe in your work or you might as well do something else.