It doesn't take £500 to clean a conservatory.
No-one's going to pay that, when it's going to look dirty again in 6 months.
I done some in the past that have been very thorough, inside, outside, roof, plastics...etc... and taken a couple of hours, and got £60 or 70 which is not bad money.
No-one's going to pay 8 or 9 times that amount.