Prices should be listed with the commonly known currency symbol that travellers will encounter when they arrive at the destination in question. Most currency symbols will usually be prefixed. Travellers should be able to assume that symbols used for multiple currencies (like $ or £) apply to the local currency. Do not use the three letter ISO 4217 currency codes like "USD", "EUR", nor "GBP" if the currency symbol is well established and commonly known:
$100 in the USA, not USD 100, US$100, 100 USD nor 100 dollars
$100 in Canada, not CAD 100, CAD$100, 100 CAD nor 100 dollars
$100 in Australia, not AUD 100, AUD$100, 100 AUD nor 100 dollars
In articles where different currencies with similar names might be confused, three letter ISO 4217 currency codes might be commonly used in an international context and tourist businesses. In that case, they can also be used on Wikitravel to avoid ambiguity.
When writing about the cost of an item in a country, stick to that country's currency. Do not switch between currencies. Doing so causes confusion and frustration. If you only know the price in dollars or euros, go to a currency conversion site and convert the number. Round off amounts appropriately. Right:You can purchase a gift for Rs 100. A taxi ride costs Rs 500. Wrong: You can purchase a gift for Rs 100. A taxi ride costs US$5.
In some countries such as Cambodia and much of Africa, the local currency is so weak or unstable that any larger prices (like, say, hotel rooms) are quoted and paid for in a foreign currency. If this is the case, follow local convention and list those prices in the foreign currency.
In some countries such as Myanmar, foreign nationals pay a US$ price for some things (hotels, air and train tickets, entrance fees), but in local currency for other things (food, shopping, buses, taxis). In this case, it is best to list the price in the currency that the foreign traveller will use even if it means switching currencies in the body of the page.
Even when the vast majority of expenses will be paid in local currency, if the inflation rate is high enough that information will become outdated in only two or less years, use the equivalent amount in US$. This should be consistent for all articles pertaining to the country.