I had a new roof put on our house back in Ky before we listed it for sale back in spring of 2017
This was a 2000 sq ft 2 story house . I dont remember the total sq ft of the roof materials wise

I had estimates from $8500 to as much as $20k if it happened all new underlayment was needed . This was the Architectural Shingles

I had a roofing guy do it on the side. Cost me $2000 plus materials , ended up in the about the $4500 range once all was said and done labor and materials . He did it on the weekends and took him and his brother 3 weekends to get it all done . This was a top over layer and not removing the one and only layer there