I agree that £3-4k is more realistic. And, unless you have registered for VAT with the view to becoming a self-employed freelance pilot, prices should include VAT. And landing fees!
You also need to factor in the costs of maintaing the rating; a minimum of two hours a year bearing in mind that, as a low-hours PPL, you are unlikely to pass a skills test with only two hours a year!
Cheers
Whirls