I find vets are more expensive here in Ontario then anywhere in the US...but so is everything else so I guess it's all relative.
Bailey was 6 when we adopted her and Katie was 7 and Bailey was more expensive health-wise but I imagine that can also contribute to adopting older pups. Katie cost us 5k as soon as we picked her up from AR because she had hookworms, something not common here. Perhaps if our vet knew what we dealing with right away we could have reduced the costs somewhat, but since she was so sick, we did everything (tests, 24 vet care) possible to save her.
Ben and Brooke, both adopted as 3 y/o have been realtively healthy. Brooke has not had any emergency care, just annual exams. Ben, at 12.5 years is starting to incur more costs because we do acupuncture ($60) when required and he gets monthly cartrophen injections which cost $35.
My point is that age may have an impact as well.