Very difficult this and that comes from an insurance broker used to dealing with this type of issue. What I would do is to get prices for flights to Tenerife using the same budget airline and see how these compare to the total cost to see if you can argue they must have been less than 60%. You could do the same for the hotel costs. Basically obtain quotes for going now which show the proprtions to help in your argument.
Not sure if it helps but worth trying. I've successfully used this tactic previously