We visited Cueva Negra campsite some years ago, just after it opened. Being brand new, it had the appearance of being quite a good campsite, but with perhaps a too-big ratio of bungalow accommodation to us touring folks. However, first impressions were somewhat diluted when considering the charges. What appeared to be a fairly reasonable basic long-term rate soon ballooned, as someone seems to have wandered around jotting down what could possibly be charged as extras. Besides the electricity (which was metered, thank goodness) I seem to recall there was a charge such things as rubbish collection, and other things which I honestly can't remember now but which left me aghast at the time.
The site itself is not ideally sited for anything, really. It was built in a rambla with maybe a partial sea view across part of the Macena ' beach' (which itself is just a scruffy collection of stoney shingle and soil), and anyone walking from the site down to the playa at Mojacar (perhaps three quarters of a mile away) along the fast road with no footpath are taking their lives in their hands.
There are four very reasonable sites in the Mojacar immediate area, any one of which would almost certainly meet most peoples particular requirements.