use strict;
use warnings;
use Template;

my $tt = Template->new({
    FILTERS => {
        commify  => \&commify,
    },
});

$tt->process(\*DATA, {
    number => 420000.2527
}) || die $tt->error();

# Perl Cookbook recipe 2.17
sub commify {
    my $text = reverse $_[0];
    $text =~ s/(\d\d\d)(?=\d)(?!\d*\.)/$1,/g;
    return scalar reverse $text;
}

__DATA__
[% number | format('%.02f') | commify %]