This may sound like a silly answer, but if your oven is electric then it shouldn't affect your gas bill.
If you meant your electric bill that will depend on the oven insulation and the amount of time the oven door is open. I don't know the typical duty cycle of a pizza oven but you could assume a high number and multiply that by the power consumption 9.5 kW.
For example if you assume the oven element is on 50% of the time at 9.5 kW for 16 hours per day at 15cent per kW then your daily bill would be $11.40. How many pizzas you make is up to you.
or for one hour $0.71.