could always rent a camper. my sister and her bf rented a splitty for around £70 for a wedding that was in the middle of nowere and everyone was camping. you could get 4 people in so bout £20 each.
this one may not be as prefered but its free. saw it on a program my mum was watching earlier. basically you put your house up on the website and then veiw other peoples houses, then once youve picked the house you message them saying you want a weekend holiday in that area and you like there house, if they like yours then you do a swap for a weekend compleatly foc.
http://www.homelink.org.uk/ also depending on when the wedding is, most universities rent out there halls for really cheep during the time students arent in, i remember someone i know getting a 5 bedroom halls house with 2 bathrooms, living room and kitchen between about 5 of them for less than £20 a night