I have had the 950's for many years They are a 20 year-old design, that's not such a problem, Stax is still selling the lambda after a longer perod of time, although Stax at least have made some design changes over that time.
The 950 phones and amp are pretty good, especially if you upgrade their 12 volt power supply. I personally use a Elenco 3amp bench supply to run the 950's.
When they were first released they sold for about $2,000.00. After a few years they dropped to $500-600 where they still fluctuate.
They are a bargain compared to American prices for Stax, however, since you can also get Stax at highly discounted prices from various Japanese suppliers, you can probably get a better Stax amp and phones for $700.00. Of course you wont get Koss' extraordinary life-time guarantee.