Quote - But I have seen the claim made -- on numbers of occasions -- that MAX needs an add-on renderer costing something in the neighborhood of $900 -- I don't recall for what purposes.  Please correct that information if it's wrong.

It's quite wrong in the fact that they claim you 'need' it..  MentalRay is about as good as it gets. The problem is in the user's knowledge of how to work it.  MentalRay is the same production-quality renderer used in Maya and XSI, and in fact XSI's core architecture itself is built around the MentalRay render engine, so that's how good it is.  There is no support for it in Cinema4d that I know of.

If for some reason you didn't like using MentalRay, then there's definitely a lot of other choices out there for Max, including Vray, Brazil, or FinalRender.  Vray is known to be much faster at rendering GI than MentalRay (at least without knowing how to use MR scripting to optimize your render pipeline, which most individual users don't know), so maybe that's what you've been reading about.

Many of the "plugin" renderers out there that are now making their way to other software did originally get their start with 3dsmax, simply because older versions of Max only provided scanline rendering, which was incredibly FAST for rendering still images or simple animations, but in itself wasn't really suitable for cenema-level production or Global Illumination renders, which the ArchViZ industry wanted/needed.  Cinema4D and Maya, for example, recently picked up FinalRender as a plugin for their software, and will soon join Max, Maya, and Truespace in acquiring the Vray renderer.  All of these incrediblly fast and high quality renderers got their start in Max.

For the person who suggested Max has a strange interface, I disagree there as well.  In fact, I turn around and say the same thing about Cinema.  Of all the highend apps, i think Max is the easiest to learn and use.  At least it was for me.  I never was fortunate enough to try all of them, but I did use Max, Cinema, and XSI for a short time.

As for buggy, well, I've heard this from some fellow Max users too.  If you're the type who likes to pile on all the tons of free plugins and addons available out there for Max, then you're going to eventually make it somewhat less stable.  Many of these plugins are not designed well, and cause crashes.  As for the app itself, it's always been one of the most stable for me over the past couple years.  I think I had one crash in the past few weeks, and yes, I was using a free plugin at the time it happened.  Go figure.