#!/usr/bin/perl

use strict;
use warnings;
use List::Util qw( sum0 );

my $hashref =
  {
    "153-1" => {
      "1069-9" => {},
      "135-1"  => { "68-4" => { cost => "300.00", cost2 => "130.00" } },
      "19-4"   => { cost => "6300.00", cost2 => "630.00" },
      "35-1"   => { "28-4" => { cost => "30.00", cost2 => "10.00" } },
    },
  };

print costof( $hashref ), " is the total where cost is found\n";

sub costof
  {
  my $href = shift;
  sum0 map /cost/ ? $href->{$_} : costof( $href->{$_} ), keys %$href;
  }