Sounds reasonable but if you would be willing, that is such an easy job to do yourself and would cost less than half of that quote. Two people can do it in half a day. That is, if you have the time and want to save a few dollars.

Edit: Oops, it took half a day for about 1800 sq ft so might take longer to do twice as much. Oh, and if you wait until Memorial Day weekend, you can probably get the insulation on sale or get a tax free weekend or something.

With that vintage house it's worth checking the air sealing prior to adding insulation. Your insulation contractor (or in many places your utility company at a much reduced cost) should go through the attic sealing anyplace that will allow air to go through-- around chimneys, plumbing, electrical boxes, and can lights primarily. This will give the best improvement per dollar spent. It will maximize the value of your added insulation.

Absolutely agree with rwiegand here. If the contractor didn't mention improving airtightness at the ceiling, you need to find a different contractor. This will have better results than simply adding more insulation, though you are on the right track by shooting for code minimum or better levels of roof insulation. Try weatherization or home performance contractors.

Air-sealing the attic on GBA

Fine Homebuilding attic weatherization resource