I’m no expert on cars, but I did used to have a Liberty GT. Some Subaru models are known to have head gasket issues. If you’re only driving it as a weekend car, I’d assume you’re giving it a decent workout and then letting it sit idle for almost a week. As Scruff pointed out, that’s not good for wear and tear.
In terms of cost, $3k is on the higher side but it can depend on what else has to be done. I’d also think that if your model has a boxer engine this may be more expensive that an ordinary head gasket replacement.