This is determined greatly by where you live. If you live any where in or around London or central Manchester, be prepared to pay a lot more than you would if you lived somewhere like Bradford! If I were you i'd get a few quotes first. Remembering that, this will give you an idea of what the person is also like, before they come into your house. I did this when I needed a new fence, & shunned the cheapest quote as he seemed to not really have a clue what he was doing, he measured up using strides, rather than a tape, & was going to overlay the old fence with the new one! The most expensive quote was given by a pushy man who dared me to go to someone cheaper, & stated that if I did, my fence would definitely blow down in the winter! His method was to overlay too! In the end I settled for the 2nd highest quote, because the man seemed genuine. My fence still stands after 4 years & is still going strong. Remember that usually cheap means just that, & over the top prices are normally put in place by people that are shoddy (unless they can provide certificates to prove otherwise), & to fool people into thinking that they will get a more superior service, when in fact they can be worse than the cheaper quotes! (I watch rogue traders!)
I had someone decorate my dining room when I first moved in. He provided the paint. Unfortunately the paint he used was very cheap & the finish looked awful, so i'd buy my own now if I were you. Also he glossed over my woodwork, but didn't clean the surface first. As a result of the previous owners smoking in there, the yellowness came through the gloss within a couple of weeks. If I were you I would sugar soap any door frames, etc that you may need glossing, before it is painted. I had to ammerite my woodwork to get rid of the yellowing!