£10 entry per adult. The only room you can visit is the grand ballroom as all others are private to the Queen. Free WiFi in the coffee shop at the gift shop end. Make sure you pick up GUEST FREE WIFI.
Although they accept debit/credit cards, make sure you take enough cash for the car park, plus £5 deposit for the audio guides. The nearest cash point is 8 miles away if the post office is closed!