However, at what point can I run the meta_value through the PHP number_format() function so I can display these 7+ digit prices with commas as I have done in my WordPress template file?
Well, it’s not possible to do that via that feature. You will need a custom code instead. There is knowledge base article here on how to do that.
The number format code should be placed below this line in that code:
if ( !empty($meta_value) ) {
..something like:
if ( !empty($meta_value) ) {
$meta_value = number_format($meta_value);