I just purchased a Rws marked 6m delivered this week in very good condition and rebuilt earlier this year. If you are fortunate to find one, make sure you check on if it's been rebuilt. I checked before hand and was quoted a price of about $250+ for rebuild and parts to do it. One was sold in GB about 2 months ago which was sold and resold as it needed to be rebuilt. If I recall, it sold for about $170 plus shipping. If you can do the rebuild yourself you still need $80-90 in parts so figure that in the cost of you go that route. I decided to wait on one that's already been rebuilt.
I have a model 10 also. If your not committed to the 6, I'd recommend you look at the 10. Better grip angle for me and feels better balanced. Awesome trigger to. Just my opinion.
Good luck in your search.