Top-end: USD$10 and upwards
USD$1 = 9000 Rial
Iran is inexpensive by international standards. A bare minimum budget for cheap hotels and Motels, Iranian food and overland transport is about USD$10 per day. Unless you thrive on discomfort, however, you should double this to around USD$20 for each days. This will provide you with decent accommodation, better food, transport by first-class (first quality) bus and shared taxi, and visits to all the important tourist attractions and cultural places. One of unfortunately parts of traveling to Iran is the dual-pricing for foreigners. This affects international ferries and flights, where all tickets must be paid for in USD dollars; tourist attractions, where foreigners pay up to 15 times as much to enter as Iranians do; and the more expensive hotels, which often charge in USD dollars.
There are 3 ways to change money (preferably USD dollars in cash): at the bank upon arrival in the airport or bank in big cities of Iran or street rate at the streets. Almost all the rates are the same, no black market anymore. Don't bother taking travelers cheques of any denomination or currency unless you absolutely must: you can only exchange them at the Melli Bank branches at the international airport (Emam Khomeini Air port) in Tehran and in central Tehran. An increasing number of mid-range hotels (and all top-end places) accept Visa or MasterCard.
In most cases, tipping is an optional reward for good service. Although there are many circumstances where a small tip is expected, you are unlikely to have a waiter hovering expectantly near your table after delivering the bill. On the other hand, it's worth remembering that helpful Iranians probably deserve some extra appreciation to supplement their meagre wages. As for bargaining, in the bazaar virtually all prices are negotiable; in shops, it's a complete waste of time. Fares in private taxis are always negotiable.