php number formating

Hello group! I am stuck and wondered if there are any php wizards that can help. I have created a custom search filter, but since I had to do a couple of functions in the code to get it to work with the Drupal filter, I now do not know how to format the numbers with a comma. i.e. 300,000. Can't figure out how to format a range function???

Here is the code for how I am building the drop down select list for the price field. *Note that I attempted to use the slider_filter, but it did not work in IE. We are willing to hire for some help on that one!