Both of those quotes seem awfully high!
I just priced out materials only for a metal roof (galvalume, standing seam, exposed fasteners, from Ideal Roofing) for my house, about 2000 square feet. Was something under $2500, and it's easy to do (much easier than shingles since it's one single piece peak to eaves and 3' wide). I did my two car garage roof a few years ago; did it myself with no help at all in two [long] days. The way the numbers worked out, doing the metal roof myself cost about the same as hiring a contractor to put shingles on. I'll probably do my house over a couple of weeks, working down the roof a couple of pieces each evening after work.
Getting the right compression on the screw gaskets isn't difficult once you find the right clutch setting on your cordless drill. I don't know about neoprene gaskets, but the modern ones are EPDM, not neoprene, and it lasts a long time.
My garage is intermittently heated, and the snow slowly slides down like a glacier, curling under as it comes off at the eaves. It never lets go all at once.