The Saudi currency is the Saudi riyal Ø±ÙØ§Ù, SAR, which trades at a fixed 3.7450 to the US dollar since 1986. The riyal is divided into 100 halalas, which are used to mark some prices, but, in practice, all payments are rounded to the nearest riyal and odds are you probably will never see any halala coins. Bills come in values of 1, 5, 10, 20, 50, 100, 200, and 500 riyals, with two series in circulation.
The riyal is also pegged to the Bahraini dinar at a 10:1 ratio. If you are considering travelling to Bahrain, virtually all businesses in Bahrain will accept riyals, but the dinar is not as easily convertible in Saudi Arabia.
Saudi Arabia is still largely a cash society, and credit card acceptance is surprisingly poor outside luxury hotels and malls. ATMs are ubiquitous, although those of many smaller banks do not accept foreign cards; Samba, SABB and ANB are probably your best bets. Moneychangers can be found in souks, but are rare elsewhere. Foreign currencies are generally not accepted by merchants.
what to buy
Few local products are of interest to tourists. Locally grown dates are of high quality, and religious paraphernalia is widely available, but almost exclusively imported. Copies of the Qur'an are produced in a wide range of editions and sold at very low prices. Zam zam water is available throughout the Western Region and at all airports.
Carpets are a favorite purchase, most of these coming from nearby Iran. Jeddah in particular has lots of carpets, many brought by pilgrims who sell them there to help finance their trip to Makkah.
Large gold and jewelry markets are prominent in all major cities. Bargaining is a norm in most small to medium sized stores. Makkah and Madinah offer a lot of variety in terms of luggage, clothing, jewelry, knick-knacks, souvenirs, toys, food, perfume, incense, and religious literature, audio, and paraphernalia.
Large, well maintained air-conditioned malls and grocery stores i.e. Safeway, Geant, Carrefour (http://www.carrefourksa.com/) are scattered throughout the kingdom.
Prices are generally fairly expensive: figure on US$50/100/200 for budget, midrange and splurge-level daily travel costs.
Tipping is generally not expected, although service staff are always happy to receive them and taxi fares are often rounded up or, not uncommonly, down. Expensive restaurants often slap on a 10% service charge, although due to lax regulation many employers simply usurp it ask your waiters if they receive any of it or not if you would like to tip them. There are no sales taxes in Saudi, and for that matter, there aren't any income taxes either!