I would go with coinwarz.com. It is one of the best for what you are looking for.
Thanks, but this one is based only on current difficulty level and doesn't seem to include the diff increase rate.
I found this one:
http://mining-profit.com/advanced-calculatorThe default diff increase rate is set at 1.10 (per month?) - is it fair assumption?
There is no ROI for cloud mining. The only way you may pull a profit is if you sell your hashing shares to some other sucker. Granted, there are a lot of those out there.
My question wasn't whether it's a good idea to invest in cloud mining or not. I'm simply interested in what's the best way to calculate the price (BTC/Ghs) when it could be profitable.