I seem to recall that Gatwick did make a thing about their own booking engine being the cheapest place to buy on-site parking at Gatwick, not sure if that’s still true.
From memory, the ‘Valet Meet & Greet’ seemed one of the best-value options to me – you get to park right next to departures, and collect from arrivals, no waiting around or buses involved, and you know your car isn’t going to be ragged off and left in a muddy field for 2 weeks, or worse.
It can also be cheaper to buy a hotel with parking than it is to get parking on its own, if that’s of any use.
I’m afraid I helped design Gatwick’s websites. I proposed a “Closest / Cheapest / Easiest” preference to make it easier for people to navigate the myriad parking options, but they didn’t like it. They seemed to think it was in their interest to leave people confused. There you go. I tried.