I would venture to suggest everything is relative. Yes, a 5 Star hotel is expensive, but does it give a better night's sleep than say a travelodge? A 5 star hotel offers certain facilities that you would not get elsewhere, and therefore have to pay for them, and like many things, even if you do not use them, you still pay for them. Caravanning is dare I say it, not an inexpensive hobby. Looking at the site fees, and gas use is only a small part of it. You have to add in the depreciation costs of both tow vehicle and caravan plus the general costs such as insurance, maintenance, road tax etc etc. Stating you need the car anyway for work, is not comparing apples with apples. If you even only travel 100 miles in a weekend away and add the whole thing up and divide by the number of nights you are away, then you have a truer cost to compare. Yes, if you use the van every day, or certainly every week of the year, then you are ameliorating your costs faster, but then again your outfits are wearing out faster.
I go caravanning because I want to, not because it is a cheap way to spend my time. In fact going to Cornwall for a couple of weeks is probably more expensive than flying to Majorca and staying in a 4 star hotel with half board, and at least you get good sunshine.
As mentioned it is all relative. If you only pop down the road 10 miles every trip, then you will spend less, but if you live in an area of natural beauty, then that can be sufficient. But if you wish to see another area, then costs rise. For me to spend a weekend in York for example will cost me close to