A dehumidifier costs around 10 cents per hour to run but could be as high as 35 cents per hour depending on your electric rates.
At 10 cents per hour if you run your dehumidifier for 8 hours a day then the dehumidifier will cost you $0.80 cents per day to run which would be around $24.00 per month if there's 30 days in the month.
If the electric costs is 35 cents per hour the cost of your electric use to run the humidifier for 8 hours per day would be $2.80 per day or $84.00 per month for 30 days of run time at 8 hours per day.
You would just have to take your electric rates and calculate the actual cost it would cost you to run your dehumidifier times how many watts your dehumidifier uses to get the actual cost for you to run the dehumidifier.