The key I believe is being able to use the paint in the most efficient way (therefore saving money on materials) and the cutting in.
We pay a decorator as the finish is superb but most of all I just can't be bothered!
It does seem however people get the wool pulled over their eyes in regards how long people quote to get things done... I'd expect my whole house painted in a week not just a room!
I buy a decent roller and duck tape and use a brush for the edges.
Usually Harris brushes and rollers.
It's not rocket science. You mix the paint pour it out and put it on the walls using the tools above.
As for finish that's usually the paints fault or you aren't rolling in a uniform direction with just a small overlap.
Or if the previous paint used caused issues like bubbling so using good paint after bad.
If anyone took a week to paint a room even a large room questions would be asked.
Even if I won the lottery I'd still paint the majority of my home myself. I'd only get a pro in to do the hallway and stairs, etc. Basically the stuff that is hard to reach and awkward to get to especially with stairs involved.
It's not the money aspect I see it as part of your job as being a man. It's also good to be up and active and feel a sense a pride of doing it yourself and taking care. Nobody ever does a just as good as you will.
Paint I get a farrow and ball Swatch take it to Johnstone's and get them to mix it up in covapluss matte or whatever it is they call it.
Even if someone offered to do it for £50 I'd rather do it myself. I remember the days when a man could change a light fixture, switch, put new wiring in, change a smoke alarm, etc.
I even do minor work on the car myself. I actually enjoy that as I'm learning stuff and I know when I take my car to a garage when they try it on. I bet the folk on here paying £800 a room or for a week's work must be getting shafted by mechanics as well.