£9.50 holiday is a base price, though. We went on one. It cost £60 for the booking (5 days/4 nights seaside holiday park), plus £16 for the bedding and £6 for bus passes for the week, and that was term time with a special deal that the nightly fee was waived and entertainment fee was free that week. Otherwise I couldn't have afforded it. But otherwise it would have been an extra £9-10 per night fee, plus £9-10 per person fee for entertainment fees. Say you have a family of four, that's up to £162, plus another £8 for bedding/bus pass as we were a family of 3, so £170 now. If they upgrade the caravan at all, it's more. If pets, more. And then there's transportation to the holiday park, incidentals, groceries (which of course you'd be paying for whether you were on holiday or not), treats for the dcs.
We ate out for 4 meals out of 5 days, so kept the food budget down pretty much. But while it's advertised as a £9.50 holiday, it obviously isn't, really.