Well, the base Hyrel System 30 printer is $3,995 on special right now with two heads thrown in, but its build area is slightly smaller than you want, so you would have to contact them for a price on a custom machine.

The special price bundles come with the basic paste extrusion head and the basic filament extrusion head. Additional print heads range from $225 to $625 depending on the capabilities. The Hyrel printers all support up to 4 simultaneous print heads, and the heads are hot-swappable.

I'm a little unclear what you mean by "Swappable extenders" and I'm a little too busy to do the math on how many mm/s print speed you want (printers are not rated by volume print rate, as that is highly variable depending on the shape being printed.)