Cost to replace spark plugs

[jasonvaughan]

Hi all, wife's car is in for a scheduled service today but as it has now done 35k miles the dealership have called and said the spark plugs are due for changing and the cost is £158.88. She has the 5 year service plan so I would have thought spark plugs would be included but even if they're not this seems a lot of money for a set of plugs and labour.
Just thought I'd post on here and see what you all think?
Thanks.
UPDATE: Garage made mistake and plugs are included in service plan.