Depends on how bad the slate roof is right now. $10k can go a long way
to just fixing the existing slate roof, and you still have a slate roof
that will probably last another 75 years, as opposed to an asphalt
shingle roof that will ned to be replaced in another 25 years.

IMO, it should be a crime to tear off a slate roof. I would say try
harder to look into fixing the existing slates. Repairing slate roofs
is becoming a dying art because everybody just wants to rip off the old
slate and put on asphalt shingles that you can get at Home Depot, every
roofer knows how to do that.

Of course if the roof is too far gone, like a tree fell on it and took
out half the roof, then that is another story. But many slate roofs
are very repairable by a slate roof expert.

Ken