price of Pontiac Montanna 2003 intake manifold repair without replacing manifold itself?

Unfortunately, that intake manifold is composite. Read that as plastic, but very good plastic. Cracking is a very common problem with GM V8s and V6's. More than likely, the manifold will need to be replaced. Besides, there are 2. An upper and lower manifold. The lower mainly just covers the lifter/cam area between the cylinders.

Don't try to fix it with stop leak or try to seal it from the outside as that will only exacerbate the situation.

Not sure what Patrick said, but you should have either the 3.1L or 3.4L engine in the Montana, I think Patrick is think of the 3.8L which did have the plastic upper intakes which had to be replaced. You can just replace the gaskets on those as long as it is either the 3.1 ot the 3.4L