Here is a thread with before and after pictures of a repaired dash. It looks nice at a reasonable price.
http://www.clublexus.com/forums/rx-second-generation/708758-new-dash-in-my-rx.html
The Lexus dealership doesn't do this type of work, so they would sub it out and mark it up 100%. Check out upholstery and leather repair shops, that is your best bet.
I own a 2007 RX350. There is a recall (9LH) on this vehicle for the VVT-1 Oil Hose which can fail destroying the engine due to lack of oil. A rear main seal failure is rare. Maybe a second opinion.