OK, I need to re-roof my home. North Texas, DFW area.

1500 sq ft, simple roof two planes, no dormers etc.
There is an add-on that is basically a raised square, roof of that is a
single plane.
There are 5 skylights, 2-ft and 5-ft approx.
Single layer of asphalt shingles, metal to be applied over that, no removal.
Pitch is 4/12, very shallow.

So I went to Mueller and got a price on materials. $4000 for R-panel.
Installation? "Should be around $2000"
By comparison, last I checked on asphalt was about $2900 total.

So now I'm ready to place the order., and the Mueller people say "$2000
is really low!"

I talk to another roofer. He says "$12,000"

At this point the whole thing is looking like a racket to me.
This is a simple job - simple enough that we're considering doing it
ourselves.

So what do I need to do to get a cost-effective metal roof?