Cost of genset and putting in?
Sorry, Gordon, your first question is a little vague. What "they are" are engine/generator sets that burn fuel to produce electrical power.
If your question refers to the kw rating, that stands for "kilowatt", which is 1000 watts. Multiply the voltage (Volts) by the current (amps) to get the wattage. A true 6kw at 120 VAC (alternating current, like in your house) would yield approximately 50 amps. BTW, 1500 watt hair dryers are not uncommon today and you could only power 4 of those at one time.
Hope that helps some, although I have no knowledge of the cost to buy and install.