The halachic pruta is equivalent to the value of 0.022 grams of silver. (0.025 grams according to a different opinion). (Source)
0.022 grams = 0.000776 ounces (Source)
0.000776 ounces silver = 5.5 agorot (Source)
0.000776 ounces silver = 1.4 cents (Source)
The price of silver, and thus the value of a pruta, may change with time. You should always be able to re-click the last two links to get an updated figure.
This was on my mind because of its relevance for maaser sheni.