It really does depend on who you get - you will need to negotiate.
My pal charges £50 per person per week (maybe less depending on how many) BUT some will charge a lot more.
Two years ago my wife and I had two days with another instructor and it cost £100 for the two of us for the two days so shop around.
Have a word with Pete and Andrea in the ski shop underneath the Markony bar near the Snowshack. (I'm sure they will do you a good deal - when are you going?)