He's worth every penny of anything up to £25m. However, we simply CAN'T spunk the entire transfer budget on one player - it's far too much of a risk for starters and we need several players, not just one. I just don't see us spending £25m this summer - I think we're gonna see some more loans.
The ideal scenario would be another year's loan for a fee of a couple million, with an option to buy for £15m-ish. Get the squad strengthened in other areas, perform well in Europe, maybe sneak the FA Cup, maybe sneak fourth place. THEN we exercise the option.