If you do not need to raise the header above the window it can reduce the cost a lot.

Most of the time the header must be raised resulting in a lot more work and damage to the interior walls.

The odds of there being electrical wires for receptacles in the room are very high.

If you have a basement they can often be dropped down from the receptacle on one side of the window, then brought back up for the next receptacle on the other side of the window.

If you do not have basement access the lines will probably need to go above the new header from one receptacle to the other.

We converted a window into a door. This is not a brick house. The house does have exterior vinyl siding, which required some addition labor to take off that siding, and then patch it appropriately after installing the door.

The proposal from the contractor was:
Door: $1158
Materials & Labor: $1200
Total: $2358.

I supplied the new inside casing for the doorway, as I wanted it to match the casings around the other doors in the room and it was not a standard pattern. I primed it. The contractor installed it. The quote did not include painting the interior casing, nor painting the wall (as I was going to paint the whole room anyway.)

We thought this was the most reasonable estimate. We had two earlier ones before we found the guy we went with: one was $3135 (which included the interior casing, but an $850 Therma-Tru door style) and the other was $3980, which was much higher, and a Pella door).

As you can see, the cost of the door is where you could have the most control as the owner. We picked an upper-end Therma-Tru door, with fancy glass.

There were 2 workers that worked a full day (8 hours), and then one worker for 3 hours the following day. That following day's work was primarily replacing the exterior siding around the new door opening.

brickeyee's point about the header is good to ask any potential contractor about. In our case, the original window header was higher than the door header was going to be, so what they did was put in a lower header, and fill in above with new drywall and plaster surface. If you have to raise the header, I can see how that would be more involved.

In our house, I could see no electrical below the original window, and as our basement ceiling is all unfinished and open, I could see exactly where the electrical lines run to that room, and was 99% sure there would be no electrical to move. (Because this is an old house, there are few receptacles in the room to begin with, and there weren't any around that window to have to deal with).

Overall, I'm happy with how it turned out. There is a very small ripple that I imagine only I notice where they had to in-fill the drywall above the new door.

If you do have the work done, one thing to make sure is that you try locking/bolting the door while the workers are still before they say the job is finished. I had my checkbook out, ready to pay the man, when it occurred to me to try locking the door. The bolt lock wouldn't close! He had to adjust something to get it to work. I am much more savvy about checking things now before they walk away. :-)

Hope this helps!
Lee