A players value is however much someone is willing to pay for him!
He was frustrating to watch sometimes, but I liked the way he always gave 110%. If he does that for Palace I am sure he will score twice as many goals in the championship - he did afterall manage 20 for Ipswich just a couple of seasons ago. In that respect he's probably worth £2.5 mill to your club, even if it is more than we had expected.