I'd personally spend the money if you can and replace the roof with a nice metal roof.
A properly installed metal roof will outlast the shingle roofs that are used.
Yes it might be cheaper to use shingles, but it's not really cheaper if you have to replace it again in 15 or 20 years.
Or if a storm takes shingles off your roof then you'll be spending money to replace them.
A metal roof will be less likely to blow off in a storm.
I'm gonna be replacing my roof in the future "About 8 years from now" and I'll be going with Metal roofing.
I want this to be the last roof I put on the old house.