This sounds like a standard 3-lens kit. I'm assuming the 150mm is a Xenar or Symmar, if it's late enough. The cams should each have the serial number of the lens on top and the camera body on the bottom, if you want to expect them to be accurate. Even if the camera has never been used, you might want to send it to someone like Richard Ritter for a rangefinder adjustment and CLA.
If the 6x7 back is a Super-Rollex with the lever wind (as opposed to a Rollex with the knob wind), and it was purchased new with the camera, that would suggest that it's one of the later versions of the III (I think there are five basic versions). The knob wind Rollex backs will have frame spacing problems with some modern films, due to the film and backing thickness, but the Super-Rollex backs don't have this problem.
Is there an aluminum case? This is often overlooked, but if you try to buy one on eBay, it's worth a few hundred dollars. Leather cases less so.
I'd say that price is reasonable, particularly if it's a III in like-new condition, since it would then have some value as a collectible.