Doing it properly no chance. not worth it.
I do it with a mate, bit of a hobby to earn a few bucks while were at it. 50 quid for a full interior and exterior clean, polish and seal by hand. Results are good and takes no time at all really, plus we use semi decent products that look good and last a while until the local car wash gets hold of it. We wet vac the seats, hoover the car and wipe down the interior with aerospace. Interior only is 30 quid which a fair few people we know locally opt for every 6 months or so, most of its word of mouth, its no regular thing, but its an easy 25 quid every so often to go in the petrol tank. We also offer machine polishes, although we rarely get these as 1. we dont have the time, and 2. people dont really understand whats going on/dont really care. Im also trying to get an unofficioal contract from a local business to maintain 2 new company cars we have recently protected for them. Bi weekly wash kind of thing, hoping to pick up a few quid from other people that work there too if they want their cars washing.
Wouldnt do it full time though. Like Dunn said, many people doing it out there, and i couldnt do professional detailing. Not a lot of money in it really.