You can create a lexical variable in the class that gets incremented in the constructor and decremented in the destructor. A class closure method makes this value accessible from outside. Don't forget to call SUPER::new in child classes.

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

{   package Car;

    my $count;

    sub new {
        my ($class, $name, $price) = @_;
        my $self = {name  => $name,
                    price => $price,
                    speed => 0};
        say 'Object car being created:';
        say "Name: $name";
        say "Price: $price\n";

        ++$count;

        return bless $self, $class
    }

    sub speed_up {
        my ($self, $acc) = @_;
        return $self->{speed} += $acc
    }

    sub slow_down {
        my ($self, $acc) = @_;
        return $self->{speed} -= $acc
    }

    sub DESTROY {
        say 'Scrap!';
        --$count
    }

    sub count {
        return $count
    }
}

{   package Car::GeneralMotors::Firebird;
    use parent -norequire => 'Car';
    sub new {
        my ($class, $price) = @_;
        $class->SUPER::new('General Motors Firebird', $price);
    }
}

my @cars;
for (1 .. 10) {
    push @cars, 'Car'->new('Peel P50', 176_000);
}

splice @cars, 0, 5;
say 'Car'->count;

say 'It works for subclasses, too:';

my $f = 'Car::GeneralMotors::Firebird'->new(200_000);
say 'Car'->count;

undef $f;
say 'Car'->count;
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