Version Upgrade

We have a customer that is using 8.0.12 with vision, no perspective. We are seeing some wonky things happen from time to time. What version can we upgrade to without incurring additional costs?

Looks to be 8.0.17, according to the downloads section.

At least 8.0.17, but you should find out whether they have total care or whatever and if upgrades are covered, in which case you should definitely go to whatever the latest 8.1.x release is.