This will vary depending on the make, model and age of the static caravan as well as the park where the caravan is sited. Some second hand caravans can be bought sited for as little as £10,000, whereas brand new ones can cost £45,000 or more and holiday lodges can cost up to £500,000. The caravan itself will be the largest expense, but there will be other costs like annual pitch fees and of course insurance. Council rates are paid by the site owner and this will be covered in your site fees.
A park owner is within their rights to ask for repairs and maintenance to be performed in a certain way, particularly when they relate to safety and the good order of the park. The park rules or the contract should make it clear what limitations there are on the park.