Well, as difficulty can influence supply and price can influence difficulty, they are at least loosely linked. You can estimate a maximum value for example for each difficulty, above which it would even pay off to rent Amazon nVidia GPU instances.

A minimum price however is more difficult to guess, as some people will even mine at a loss or don't even face losses when mining, because they dont pay for the electricity themselves.

Currently it looks like 3 difficulty increases ago that a few miners at least suspoend their operations. Noone know if this will continue though. Another factor is that in the past few days much lesss than the daily mining income worldwide was traded on exchanges. This puts quite some pressure on the more nervous "I-have-to-sell-each-day" miners to get rid of their earnings and leaves a lot of other miners with full bags of Bitcoins that they want to get rid of. As you see, they get a bit more careless (a lot of "double trouble" games in the Marketplace popping up) - might even be a good thing, if they now start to use it more as money than as "gold"?