I doubt very much it is just the £2.5k a week difference in salary. There is bound to be a signing on fee. If they paid him £200k that is still considerably cheaper than having to pay a transfer fee for him.
This must be one of the dumbest yet. Murray is an employee of the Albion. Why are there so many niaive supporters who expect players to bleed blue and white for he Albion. Every single one of them, as well as Gus, would be off for the right offer. Murray had a shit time to start with when...