If it is truly NOS and you can document that fact, it could be worth $1000s. Good luck.
I have a similar story, a friend gave me a TD124 in a paper bag for free. I built a plinth out of nice black walnut and I used a well tempered arm with a Denon 103R. The turntable worked great, but the sound was not any where close to what I was getting with my modified well tempered table with a low output benz glider. I blame the 103R for this, it is a great cart. for the money, but the glider at $1000 kills it. I would invest in a better cart. and preamp., consider buying used on Audiogon for a nice discount. I am now selling the glider (listed at $450) and I have sold the Thorens on Audiogon for $850, I was expecting to get more since it included the plinth and arm board, but there was no interest at $1200 and $1000. So I think the best you will get for the 124 is may be $900, unless the new in box is very attractive to buyers. I purchased a benz Ruby 3S here for $1300 and it is much better than the glider. So I would definitely invest in a better cart.
Good luck and have fun.
Thanks for your advice. I tend to lean in your direction. Now the matter of how much I should ask for it: Since it doesnot happen often that these are offered n.o.s. I have no clue yet what this is worth. You said about 900, someone else 1000's. It would also be the very first item I put up for sale on audiogon. A flying start but no feedback whatsoever. Thanks again,