C:\>perl -e "print '1,000,000' + 1000"
1001
C:\>

##</code><code>##

sub decommify { 
    my ( $number ) = @_;
    $number =~ tr/,//d;
  return $number
}

sub commify {
    my ( $number ) = @_;
  return undef unless $number;
    ( $number, my $dec ) = $number =~ m!([+-]?\d+)\.?(\d*)!;
  return undef unless $number;
    $number =~ s/(\d)(?=(\d{3})+(\D|$))/$1,/g if length($number) > 3;
  return $dec ? "$number.$dec" : $number;
}

print commify( decommify("1,000,001.123456789") + 1000 );

__DATA__
1,001,001.12345679