I’ve got an 03 Impala with 125k miles on it. It’s got minimal Midwest rust on the body, but otherwise in good shape. I’ve recently found out that the cylinder head is blown and will need replaced. Would it be worthwhile to fix? If not, how much could I sell it for as is?

 

if the head gasket is blown and the heads are warped they will need machining ...maybe $1000 for machining both heads plus $1000 to do the head gasket. worst case there could be more damage if it was run to long with no coolant.
quote it out at some shops near you and quote a used engine; see what is the better option.

in my region a car of that vintage not running....sell for $500 tp $1000 depending on the trim level and body and paint shape.