The Daily Fail believe it's ten million pounds!
http://www.dailymail.co.uk/sport/article-2320978/Mike-Ashley-pay-Alan-Pardew-10m-sacks-Newcastle-manager-year-deal-Charles-Sale.html
Newcastle will have a WHOPPING contract to pay off if they sack Pardew though, if he is ousted they'll have negotiated an agreement of some sort to lessen the financial drain
It really is astonishing how they got 5th under him and with that squad, shouldn't do too badly this season though, mid table would be a good final result for them