I fixed my visa up through this site www.uppersia.com which I found on the internet. They got the papers through in about a month: they were friendly, cheap. I could then get the Iranian visa on the spot in Paris. You have to pick up the visa then within 3 months, and its valid for an entry within 3 months of you getting the visa. I recommend their services very much.
For Iran visa you should fill in the visa form on Iran visa application , it takes about 3-7 working days to get your reference number and two working days to collect your visa at the embassy by direct referral or one working week by posting the docs to the embassy. You can pay the visa fee in cash in Iran.
Check the cheapest Iran tours.