Subarus of that age with the 2.5 liter engine are known for having head gasket problems. Ours started leaking at about the same mileage as yours. The repair bill was about $1,500. Unless you repair it, your Forester will be impossible to sell. Although there is no guarantee that it won’t cost you more money in the future, I don’t see how you can get by any cheaper. Anything you buy for the cost of Subaru repairs will be in worse shape than your own car and will also need expensive repairs.