Do the formatting in a sub:

use warnings;
use strict;

print "Current Account Balance: ", asDollars ($_), "\n"
    for 100000000, 100, 1000;


sub asDollars {
    my $value = reverse sprintf '$%.2f', shift;
    $value =~ s/(\d{3})(?=\d)/$1,/g;
    return scalar reverse $value;
}
[download]

Prints:

Current Account Balance: $100,000,000.00
Current Account Balance: $100.00
Current Account Balance: $1,000.00
[download]

Note that scalar is required in the return statement because reverse may otherwise see a list context.