What is the current actual cost of mining 1BTC? Bitcoin is going down right now. It's about 500USD/BTC. I wonder what is mental support price for miners under which they would prefer to buy btc instead of mining it? That would be more or less mining cost. So what is the current actual cost of mining 1BTC?
You can use a mining calculator to compare the available hardware's output, then add fixed cost (hardware) and variable cost (the cost of manpower, power, replacements, maintenance, etc).

I am assuming you mean ASIC mining cost, as GPU mining has not been profitable for bitcoin for quite some time. I found a site which keeps track of ASIC deployment and also provides a mining calculator: http://minr.info/

Generally miners do a lot of work to find places with cheap power, you can find kWh rates here: http://en.wikipedia.org/wiki/Electricity_pricing#Price_comparison

Even though this may seem unrelated, miners can also use GPU or Scrypt ASICs to generate alternate coins (and then convert them to bitcoin), which may be cheaper than generating/buying bitcoins. You can find a lot of information about various algorithms and a mining calculator for many alternative algorithms here: http://www.coinwarz.com/cryptocurrency

Beyond all of this, it is worth noting that bitcoins can be generated by any computer capable of doing such calculations, and that there are at least some people who do not pay for the power that they consume, and sometimes not even the hardware (such as college students and hackers, respectively). Therefore the price of mining a bitcoin can be next to nothing or actually nothing for some people who do not play fairly, and who will mine full-force at virtually any price.