从echo语句中显示的值中减去一个数字

I am using this code to echo a number

<?php echo Mage::helper('core')->currency($_product->getFinalPrice(),true,false); ?>

The output looks something like $1850.00

What I want to do is instantly subtract $720.00 from the amount shown.

Is it better to do it with php or with jquery? I am imagining the code will be really simple... please show me:

If you purely want to echo the lower value, then;

<?php echo Mage::helper('core')->currency(($_product->getFinalPrice()-720),true,false); ?>

The products price will still be $1850 if it's added to the basket though.