At Price's Market, four oranges cost one dollar. How much, in dollars, will 10 oranges cost at Price's Market?
We have the ratio $4 \text{ oranges} : \$1$. Multiplying both sides by 5, we get $20 \text{ oranges} : \$5$. Dividing by 2, we get $10 \text{ oranges} : \$2.50$. Thus, 10 oranges at Price's Market cost $\boxed{\$2.50}$.