Depends on how you get there / where you stay / what you consume etc etc.
This year we opted to drive the straightest route (Payage) return fuel to Wales – £240
Chunnel – £120 return
Payage – £70
We took our tent and camped £90 for the week
We cooked our own grub mostly and ate out a couple of times £150 for two for the week
Lift pass – £150 for two
All told about £500 each for a mega week of fun
You could fly cheaper and combine with a Chalet / All inclusive but I reckon it would be about the same costings