Looks like a late '30s model. Certainly not a rare machine, but like many brands how many you find locally is very dependent on where you live. I quite like the optional language keys it was fitted with, which isn't as common. I'd love to see a sharp image of a slug that shows the typeface stamping.

Hmmm... 

This is a very rare typewriter and in this condition its unheard of.

 

There's no point in my disputing your sales hyperbole since someone already bid $150 USD on it. I find that amount to be stunning even though I shouldn't be surprised; I know of a few buyers/collectors around here who regularly overpay for typewriters too. Good luck with your sale.

Pricing isn't based on its age (I have a number of typewriters that are much older and paid a fraction of what your machine sold for) or what it would cost to make today; like so many other things that are collected, pricing is determined by supply and demand. The aesthetic condition of your machine is decent, but not great, and it's certainly not a rare model, so I know that I could buy one for far less. And all of that is ignoring the bigger concern, which is the Rheinmetall's mechanical condition.

There are of course those who don't have a clue as to the value of these machines, and even some who should know better but still overpay, and those are the people who you would hope to find when selling a machine on eBay. I think you did rather well with your sale.