If it's just a head gasket, surely you can do that yourself? It's not a hard job. And the local shop will put tubes in the tires, but tires with a slow leak aren't exactly something that will stop someone buying it. The head gasket is the real issue.
Otherwise, as people have said, less than $2K will move it to a reasonably happy buyer. They might be really happy because they do the head gasket themselves and it's all good, or only moderately happy if it turns out they need to put $1k or so into it for other unspecified issues.