One could in theory offer up an M6 for say $3,000 simply because of greed, but that doesn’t mean someone will accept the offer.
M6s have hovered around $1000-$1200 for the last decade for those in good condition, with TTL a bit higher. Prices are definitely up, as the supply up for sale is the same (or less) and the demand is higher. In any case the D/S ratio is higher.
What's amazing to me is how low the Hexar RF is, considering it's the only M body with 1/4000, and how high the Zeiss Ikon has gone.
Both situations are supply/demand, but if I were in the market I'd get a Hexar.