You know what the funniest thing about that line is? They really did rent a castle, not build a model. Renting the castle was, in fact, the biggest item in the production budget, followed by the rabbit launch. After that, they couldn't afford horses, and that's how the coconuts happened.

And yes, Monty Python and the Holy Grail is surely one of the most quotable movies in existence.

"Strange women lying in ponds distributing swords is no basis for a system of government!"