Unless you've dealt with the 3.4 DOHC, I wouldn't bother. That head gasket will morph into all sorts of evil. It will most likely end up exceeding the value of the car. Go to
www.nada.com and punch in your zip code and the car model incl mileage. For example I did it for my area and used 90k miles (probably lower than this car has) and it showed $2800 average retail.