National Express seem to be still taking bookings online...going from Barnsley Interchange at 9.20am, returning 18.45....£28. I'm no help with any other coach firms I'm afraid http://www.nationalexpress.com/coach/destinations/events/facupsemi.cfm
According to website, should get to Wembley for 1.30pm...I bloody hope so...was thinking of booking tickets with National Express myself!
That thought did cross my mind too.... ...There was a post earlier on asking about coaches....the replies to it might be some help http://www.barnsleyfc.org.uk/bbs/forums/thread-view.asp?tid=103776&mid=670302#M670302