The site determines the cost of the caravan or lodge, not just the fees. It is really difficult to find an actual price for comparison nowadays, as a lot of the manufacturers are linked to the site owners, too.
Ours was about £75k, and is far from the top of the range model, but the site can charge a premium because of its location. We love it, though - it is a 2 bed lodge with a bath and shower, which is more than big enough for 2 of us. The main bedroom is spacious, and having a bath is a real luxury compared to caravans I knew as a child
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Something else to bear in mind is that lodges in particular come unfurnished, so as well as the price to buy it, you have to fork out for that, too. The upside, of course, is that you furnish them to your own taste, and could, potentially, take things with you if you sell it on.
Which leads to another consideration. If we ever did decide to let ours go, we would have vast amounts of things to re-home, from duvets and plates to bookcases and things like a coffee table and sideboard, plus all the kitchen equipment we have acquired over the years - a microwave, magimix, slow cooker etc. They are great to have when you are there for a while, but we don't need two of each at home, and there is no saying that a buyer would want that sort of thing.