SciFinderⁿ (first time? Register first) provides listings for the commercial suppliers of chemicals, and many of these suppliers provide pricing details.

Sign into SciFinderⁿ, then

• click the Substances button
• search for your chemical by chemical structure, molecular formula or other substance identifier
• for the chemical you want, click the Suppliers button and apply any filters in the left-hand pane
• the Purchasing Details column lists quantities and often prices, though for some listings you may need to click the “Product Information” or “Order From Supplier” link to view prices.

ChemSpider, a free chemical database, also links to commercial supplier listings which may include pricing details

• search for a substance (by name or structure)
• scroll down to "Chemical Vendors" and expand the section
• try the "External ID" links.

N.B. If no currency is listed, the price is probably in US Dollars.