Greenbelt is a long way from Staten Island, home of Villa Marin Cadillac.
For a 2002 Seville, the intake manifold R&R is 2.5 hours, so add another .5 for the intake plenum, a $43 dealer-only part, and go from there.
DIY is a few hours, nothing magic, and the (dealer) plenum and a set of intake manifold gaskets.....get them from
www.rockauto.com (expensive at the dealer).