TT used those numbers with the aim of getting you to shut the [expletive] up when seeing it laid out in front of you. Yeah, I don't know why he thought that'd work either.
Castro isn't a really expletive good player yet. He projects well, but by the time he gets there, he probably won't be that cheap anymore. No, he'll still be cheap next year.
Unless the Cubs plan on skyrocketing the payroll, there is no reason to trade a league minimum really [expletive] good player unless you're getting a league minimum really [expletive] good player in return.