A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Money
Numbers
Part III. Style 20 spelling

U.S. CURRENCY. If you refer only occasionally to U.S. currency, follow the general rule (see 23.1.1), and spell out the words dollars and cents. Otherwise use numerals along with the symbol $ or ¢. Omit the decimal point and following zeros for whole-dollar amounts, unless you refer to fractional amounts as well.

Rarely do they spend more than five dollars a week on recreation.

The report showed $135 collected in fines.

After peaking at $200.00, shares of the stock plummeted to $36.75.

Express large round numbers in a combination of numerals and words.

The deficit that year was $420 billion.

OTHER CURRENCIES. For currencies other than that of the United States, follow the pattern for the U.S. dollar. Most currencies put unit symbols before numerals. Even though European nations represent decimal points with commas instead of periods, you may use periods, except in direct quotations from sources.

When she returned, she had barely fifty euros to her name.

The household records show that it cost only £36.50.

Its current estimated worth is ¥377 million.

Most European nations now use the unified currency called the euro (€), but if you are writing about topics from the period before 2002, you may encounter such currencies as the French franc (F), German deutsche mark (DM), and Italian lira (Lit). British currency is still expressed in pounds (£) and pence (p.), though before decimalization in 1971, it was expressed in pounds, shillings, and pence (for example, £12 17s. 6d.). Note that billion in traditional British usage means a million million, not a thousand million; to avoid confusion, do not use billion for British sums.

If you are unfamiliar with the conventions of a particular currency, consult a reliable authority.