http://php.net/manual/en/function.number-format.php
there is this page with some simple php code on it ? I am guessing it is in php is it ? and you want to apply it to the price section of the account?
Can I ask if why you have not just built a simple $ field or adjusted the one you have and changed the options at the end from UK, AU etc as in currency to $ amounts such as K, M, etc ?
so they would type in 1.2 and then select from the dial up 1.2 K or 1.2 M etc so the customer ads it as it should be ? just add to help the information / example on using price section.