If it were my house and I were ready to “do it” I would take off the drywall on the garage side first to see what I was dealing with. Whether you do it yourself or have someone else do it, you need to see what is there. If the contractor can’t see it, the quote will be littered with “if this, then this, yada yada.” If he can see it, it will be easy to estimate.
If there is no plumbing or electrical, it’s pretty easy.
Sometimes, you can frame the whole door without disturbing the drywall on the interior side, then just cut away the drywall inside the frame after the framing is done. Sometimes, not.
After you cut away the drywall and see the project, order a pre-hung door. 1-hr Fire door w/ closing hinge is the code, I think. Dixieline will help get the right thing, right swing direction, etc. Think about which side the hinges go on.
Add full-length studs on the outside (start about 8″ wider than the door size, if I recall), plus a header support inside of those. Put in the header and make sure you replace the studs above the header to keep that support in place.
Once framed, re-route any plumbing or electrical.
Then, hang the door.
Then, put in moulding around the door to finish it.
I know a framer that works for $200 a day that would do this for me (for me, not for you. Sorry) in a single day – frame it and hang it. I would finish up the moulding myself.
I could see a plumber and electrician costing two or three-hundred each.
Need a good carpenter to hand and finish the door. I do this myself so I’m not sure what it would cost.
Call it $500.
With no plumbing/electrical – call it $300 for the door. $200 for framing and hanging. $500 for finish work = $1000. Add $600 for plumbing and electrical. A “full-service” one-stop-shop contractor would probably charge you $2K or more. I like to find my own “little guys” to do each part.
As ado-it-yourself project, this would cost me about $500 in door, lumber, moulding, and paint and take maybe two weekends.
