It's not expensive. In fact, it is free if you're going to release free games, using the Visual3D engine.
Visual3D.NET is an all-in-one IDE/Build tool built on top of Microsoft's XNA platform which out of the gate will allow the use of two different .NET engines.
There is the
Suva3D engine, which I'm told by the Visual3D guys is
very expensive, or the Visual3D engine (sort of an updated and more powerful version of Axiom, the OGRE .NET port - the maker of Axiom is on the Visual3D.NET development team). The Visual3D engine will be affordable to indie developers wishing to release commercial applications, I'm told.