Most lenders will require the seller replace it as a condition of the sale. I'd also want to know why the roof has failed. Holes in metal are unusual. Rust in a good quality metal is unusual as well. A good metal roof should last much longer. Even in coastal conditions.

Pricing on roofing depends on more than just square footage. It depends on how steep it is, how many cross gables and other valleys that will need flashing, the condition of the roof sheathing, and the quality of the material itself. You could pay from 5-15K for a roof for a similar sized home going from a plain ranch with crap that won't last 10 years to some pretty good architectural shingles that will last 30 years on a pretty steep and complex roof.