If I have both 110V and 220V outlets at home and I am going to buy an electric appliances (freg, TV, Receivers, DVD players... etc), is their and advantage of one over the other, since I have the option of buying 110V or 220V. I am mostly interested in cost.

Do you mean the cost of the appliances, or cost of energy to operate the appliances?

Cost of energy will be the same, a watt is a watt.

Be sure to match the frequency of any appliance or device to the system you have.

If you want to be safer from electrical shocks then use the 110V

As tkrussell said, match the frequencys its important