I think he was talking an established player off the 25, not another prospect.
But my point is no team acquiring a player like Sale is gonna do that. The reason you trade for Sale is because you're trying to win a world series. Trading a valuable piece off your current MLB roster is one step forward two steps back. For example, let's say you're talking about Betts or Bogaerts. Right now they are worth 5 fWAR and 2.6 fWAR respectively. Sale has been worth 8.2 So while true you're improving in both cases, you then have to look at the alternative. Who do you plug in at SS if you deal Bogaerts? The sox don't have that answer as such they aren't dealing him. With Betts you can sorta shuffle some stuff around but the point here is that trading prospects costs them nothing toward 2017 and thus makes them a better team this year. They are going to win between 90-95 games this year but if you're subtracting 2-3 wins for whomever replaces Betts/Bogaerts you're a far less effective team.
That's why no team is going to trade an established player like that. So it's fine to suggest the idea in theory but in practice it's not going to happen. It's the same reason Theo and company suggested they weren't trading anyone off the cubs active roster this year in order to acquire Quintana/Verlander/whomever. Additionally, let's say the white sox drew a line in the sand on Betts/Moncada. What team in the majors matches that sort of offer? You're talking about a 5 win player and a top 5 prospect. Boston is probably the only team who can match that. Even if you lower it to Bogaerts and Moncada, there's few teams who have an all star SS and a top 5 prospect to trade.
In other words, the white sox don't have the leverage to pull that off because no one can offer more than that demand to drive up prices. What Sale is worth is irrelevant. It's what teams have to trade for him that matters because you have to have multiple teams with high level prospects/players in order to create a market. Boston isn't just going to bid against themselves and pay whatever the Sox want. We sort of saw this with Q. Houston was in talks to acquire him prior to the start of the season and the rumor then was the sox wanted Martes, Musgrove and Tucker. They ended up getting a decent return in Cease/Jiminez but they aren't as valuable as the Houston package they reportedly asked for. And ultimately in the case of Houston there was no one else offering anything near that in order to entice Houston to pay more.
I imagine the sox probably did ask for something ridiculous for Sale. I believe Theo mentioned any talks on the cubs end started with Bryant or no deal at all. So, it's not like Hahn was lowballing people here. It's just that if Boston says no to Betts what other choice do the white soxs have? They either keep Sale on a bad team and his great contract loses another year or you lower the price on him and get what you can speeding up your rebuild. Even if they held on to Sale to the trade deadline I don't think they get more and of course you risk Sale pitching poorly/getting hurt.