I don't know about super rich vacationers, but the prices you are likely seeing reflect that Torquay is a prime (south coast seaside) holiday destination (for the UK), and you're looking for an entire month during the height of tourist season there - during school holidays. It could also be that more affordable lets are already booked up for families on school holidays.
Just taking a wild guess, as I've not priced south coast self-catering places this year nor for south coast in July, but paying minimum of £500-750, per week, for what you're looking for - fairly normal. My guess may well be too conservative even. Tote that up for a month & it's a lot of money, yes!
We tend to visit in 'shoulder' season periods or go to less popular destinations to get more affordable self-catering holiday prices.
Good luck!