If you go with a large breed I'd make sure to buy only from a reputable breeder that can show lineage without signs of hip/elbow dysplasia and who breeds for conformation to breed standards not for mega size.
Big dogs already are predisposed to joint problems, it only makes it worse when dumbass backyard breeders purposely breed for sizes larger than they should be.
I spent almost $1500 on my Rott but he comes from a long line of Champions and they guaranteed him for 2 years against dysplasia, they would have taken him back and given me another one. Not that I'd have taken them up on it, but it shows their commitment to breeding healthy dogs.
Their lifespans are already short enough at roughly 9 years, I wanted to be sure to get one with as healthy genes as possible so he could have a great long healthy life.