High price, definitely. Is it a hip or gable roof? Hip roof = much more complicated and expensive.

Not sure if roofing products are the same there as Canada. Uncoloured metal, which I expect you are referring to, is "galvalume", an alloy of steel and aluminum. It costs about 1/3 less than coloured metal roofing--installation costs are the same.

Metal roofing is definitely more cost-effective than shingles--faster to apply and lasts VERY much longer without the environmental costs of getting rid of the old. Also, doesn't need full-sheet underlay since it can be installed over strapping--again a cost-saving.   

When you say "some wood will need to be replaced", that could mean anything and is it possible that the quote was high to include worst-case scenario (new trusses/rafters/chimney and all)? Dormers are perennial problems--removing it and roofing over the hole is quite easy, replacing it is not. Looked into sunroofs?--they have come a long way.

If another contractor gives you a similar quote, I would step back and consider your long-range plans for the house--for that kind of money you might as well get more ambitious and do a full reno, add a storey or whatever you think will be most valuable 10-20 years from now.

W-O