You have to set your own pricing Sky' but I'd avoid mentioning " minimum price " to clients as it can give them something to object to.Just price by the job but try to avoid dropping below what you regard as the minimum you'd work for.I personally reckon a minimum of £50 is fine.
Went and did a job today at a 4 star hotel in the New Forest , the rooms are of a very high standard , 3 years ago they were £80/night , tonight you can stay for £30 , if you need work prices have to come down in this climate to stay profitable. If you dont need the work , raise them.