Correct answer. Another possible way:
<tr>
<th>Price:</th>
<td>
<span itemprop="price">$137</span>
(<abbr title="United States Dollars" itemprop="priceCurrency">USD</abbr>)
</td>
</tr>
Due to the fact that "USD" will be visible to the website visitor, you will eliminate any possible confusion for your visitor regarding the currency that "$" refers to (US dollars, Canadian dollars, Australian dollars, etc.).
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