Displaying content from 2 different fields

Hi all

I have a bit of a problem

I have 2 fields (display_price & used_price)

The display price always has a price but it is higher than the used price field, but not all records have a used_price instead, the used_price field always contains a 0.

How can I write a code so it will displays the used_price field results, if there exists one higher than 0, but also if the display_price has a higher price ?

//if used price is greater than 0 and display price is greater than used price
if ($used_price > 0 && $display_price > $used_price) {
echo $used price;
}

This kind of worked, except I might have forgotten to add, what if used_price has a value of 0, but display_price has a value, lets say $20.00

How can I get to display $20.00