sub format_float
{
    $val = shift;
    $intgr = int( $val );
    $fract = sprintf( "%2.2d", 100 * abs( $val  - $intgr ));
    if ( length( $intgr ) > 3 ) {
	while ( $intgr =~ /\d{4,}/ ) { $intgr =~ s/(\d{3})\b/.$1/ }
    }
    join( ",", $intgr, $fract );
}

foreach ( 10.5, 4000.8, "100000.000", 80000, "80000", 
      36000.0000, "36000.0000", 12725.0000, "12725.0000" )
{
    print "$_ => " . format_float( $_ ) . "\n";
}