The number I've heard that Barnsley want is £600k - but that number was from before they were relegated. Whether they'll want more or less now, or whether they'll refuse to let him go to use him in their own L1 campaign I have no idea.
Personally, I don't think Kane is worth paying £600k for. That level of money buys you 2-3 really solid L1 players and I think we need to prioritise filling the defensive positions far more. We've got Henry, Bodin, McGuane and Smyth (and hopefully Brannagan) who can play CM, and the first 3 are all forward thinking, more attack minded midfielders, just like Kane. A proper CDM and a powerful box to box midfielder are far more important for this side than a Herbie Kane type player, as good as I think he is in CM.