Here you go...

#!/usr/bin/perl -w
use strict;
use CGI::Carp qw(fatalsToBrowser);
use CGI qw(:standard);

my %_numbers = (
    1 => "2020283.40",
    2 => "02384829.94",
    3 => "1038.92",
    4 => "303.02",
);

print header();
foreach my $num (sort {$a <=> $b} keys %_numbers) {
    my $_number = format_number(sprintf('$%.2f', $_numbers{$num}));
    print qq~$num) $_number~, br();
}

sub format_number
{
    my $num = shift;
    $_ = reverse $num;
    s/(\d{3})(?=\d)(?!\d*\.)/$1,/g;
    return (reverse $_);
}
[download]

That yeilds the following output:
1) $2,020,283.40
2) $2,384,829.94
3) $1,038.92
4) $303.02