You can check approximate Iran Visa Fees for all nationalities here. The visa fee is paid on the day, you want to go to the embassy after you get your reference number. The visa fee should be paid to the Iranian embassy in form of bank draft or by credit card. It has nothing to do with the visa reference code charge that you pay to ITS or other official agencies.
Disclaimer: The fees given here are approximate and based on previous visa fees. They are intended to give you how much you have to spend on visa. So they are by no means absolute figures. Iran Travel Service is not responsible for any inconviniences due to the approximations or mis-figures. Always check everything with the consulate on phone. Even the site can be outdated in most cases.