The last garage that I built of my own took 30 days from the day I got the permit until the final inspection. That was including the electric, and all done by myself, except that I had a friend help me put the last sheet of plywood on the roof.
I have someone lined up to do the concrete for me. He says that it will be 2 to 3 weeks before he can do it, but the temp has to be aleast 34 deg. I had hoped to have this done before now to avoid the temp problems.
They have made a few changes to the building codes in the last few years. Mainly in the area of storm strengthening, like anchor bolts and nailing sheeting. Nothing to justify the high costs that the contractors are quoting. Once the concrete work is done, it should take me about 2-3 days to get it weather tight, except for the shingles. I have a brother that said that he would take care of them.
If I was about 20 years younger, I would start a business building garages. I could build them for 1/2 the cost that these people are quoting and still make big bucks.