A very accurate equation to find the bottom of the barrel price is to figure the electric cost for 10,000 bbp per month and thats usually where the price will be on the exchange without forward growth. (IE the electric arb rate).
Since we are CPU mined, thats about $20 for 10,000 bbp.
It works because miners who pay $20 for something are reluctant to sell lower than this rate, therefore coins accumulate until the arb rate is at a minimum surpassed.
In the long run it should work out like that. That's the nice thing about PoW - there's a fiat cost associated with every coin that's mined which provides a degree of stability to its market value. Additionally, the more people that are actively mining, the higher that fiat cost per coin (coins are being generated at the same rate, but now there's more hashing power behind every coin representing a higher fiat cost going into each coin), so the higher their value.
Right now, there's a lot of people who mined a lot back when the difficulty was pretty low, though. If they think think they can increase their profits by investing that value elsewhere or by using it to margin trade, they'e going to be willing to dump at a lower value since they had negligible costs in the first place. I think we've already passed the "free coins" phase, though, so within a couple months anyone who was planning on dumping will probably have dumped.