1Mh/s can mine ~600 coins in a day.
1Mh/s can earn about 0.005 BTC per day.
So the price is 0.005/600=833 satoshi.
However the difficulty is not "normal" now.
Time per block for the whole network is 82 seconds.
The normal time should be 120 seconds.
The difference is ~46%.
So the normal price should be 833satoshi X 1.46=1220 satoshi.
Everything under 1220 satoshi worth to buy.
Correct me if I am wrong
You are wrong . Current difficulty has nothing to do with the price or the value of a coin, but has to do with the costs. Also the diff retarget is very retarded, so there was a lot of instamining last night. What you are referring to is the costs but I would buy only ~400 even if the cost of producing today is higher, now if the diff stays this high for more than a couple of days then I might think different but is too soon to know.
Cheers!