The currency in Iran is the Rial, and there are about 30,000 Rials to the US Dollar. Most prices that you will see in shops and that shopkeepers will discuss with you will be given in Tomas. One Toman equals 10/ Rials. Therefore, an item that cost 10,000 Tomans is actually 100,000 Rials, or about 3.0 Dollars
You should change money at airport bank, or hotel bank, to cover expenses not included in the tour cost and for personal expenses. You can pay Dollars/Euros for any purchases of handicrafts, carpets, etc. and for tipping drivers and guides. There are no preferences between Dollars and Euros, and both are equally accepted.
You can bring cash US Dollars/Euros and there is no restriction on the amount (although, officially, it is $6000.00), and no problem in taking out what is left!
Please note that no credit cards are accepted here for any purpose. Some of the more prestigious carpet shops in Isfahan, with overseas accounts, might accept credit cards for substantial purchases, but we cannot commit to this.