We have never been a member of the C&MC so cannot comment.
We have been a member of the CCC for the 8 years we have had a van. I have an "app" on my phone and on this computer which tells me when, where and price for their "meets". I use these all the time to stay somewhere or to stop for the night when travelling distance. Most meets are not pre-book so one can look at the weather forecast on a Thursday (or any other day) pick a location we fancy and (after phoning just to check that the meet is on) set off on Friday morning for a cheap weekend. Prices are usually under £10/night and as low as £4/night. Meets are usually over a weekend but can extent to 5 nights but as has already been mentioned, Temporary Holiday Sites (THS) can last up to a month. The meet can be in a field with only water and elsan or can be on a site (usually out of season) with full facilities.
One example I used last year was Kirkby Lonsdale RUFC. They are a site with facilities and charged £17.50/night (ehu was extra). I stayed there in August for £10/night (ehu extra) with a meet organised by CCC. Same site, nearly 1/2 price!
If we use a ferry then the cost of membership is paid for (and more, on expensive crossings).
The meets usually have a hall and entertainment is usually laid on usually just Saturday evening. There is no compulsion to go into the hall and join the other "campers".
Before Christmas we attended a meet at York racecourse from Friday until Sunday and went Christmas shopping at York Christmas markets. On Saturday evening entertainment was laid on in the racecourse complex. Cost for the two nights and entertainment was £25.
Most members don't use the meets for cheap stays and I have no idea why.
We hardly ever use "proper" sites as they are too expensive. Unless I really have to, I won't pay more than £10/night to stay somewhere. (Yes we did in York, but £12.50/night in York is cheap!)
Happy New Year, Dave.