tappets on mini Cooper s turbo

[mjw0321]

Hi. My gfs mini has been playing up for a while. It seems to drink oil and often the power dips when you floor it. More recently it started making a lot of noise (almost like a hole in the exhaust) and performance dropped. It is in the garage now. The car has done 90k miles. The garage has said they think it is the tappets and that 16 need replacing at a cost of £700. Any thoughts/advice on this? I know nothing about engines so any advice or suggestions will be great fully received!

[mjw0321]

They are saying it is 5 hours of labour. This seems very high. A Google search shows that on other cars it seems to be between 1 and 2 hours. Any thoughts?