Depends on the condition of the door casing, if any/all ironmongery is supplied (and what type), whether or not it"s a solid oak door or a veneered and lipped one, the value of the door, and where abouts you are in the UK. Amongst other factors
And even then any carpenter worth their salt won't quote blind, but will want to see the job for him/herself. If they don't then caveat emptor!