Always quote prices in US Dollars, unless you’re specifically referring to a regional cost, or a product/service only available in a particular region.
Use the $ symbol: $20.
Don’t use decimals unless cents are included, e.g. $20.50 but not $20.00.
Don’t use ‘$0.xxm’ for amounts less than $1 million.
Write out ‘cents’ in full: ‘it costs 8 cents per minute to call the support line’.