What costs less central ac on 220 volts or window ac on 220 volts?

The answer is: "It depends". . . .

How big a space are you trying to cool?

How hot does it get?

How cold do you want to make it?

The reason "it depends" is because 220v AC units are typically much more powerful than the corresponding 110v units - you can check this by looking at the cooling capacity rating - in the US, measured in "BTU"s - the more "BTU"s of cooling, the more powerful the air conditioner.

On one hand, trying to use a smallish "5,000 BTU" window unit (typically 110 volts) to cool a large living area that gets rather hot is an exercise in futility. You can run it - consuming electricity - until the cows come home and it may never do the job.

On the other hand, using a 30k / 40k BTU "wall unit" 220 v AC unit in a 9x12 bedroom will rapidly turn it into a deep-freeze - and waste energy in the process.

Once you decide how big an area you want to cool - in square feet - any reputable appliance dealer should be able to help you pick out a unit correctly sized for the space.