- chunk_split: documentation ( source)
- substr_replace: documentation ( source)
<?php
$price = 9987536453;
$last_digit = (string)$price[-1];
echo $last_digit."<br />\n";
$price = substr_replace($price, "", -1, 1);
$price = chunk_split($price, 2, ",").$last_digit;
echo $price;