Laravel relationship through a parent

I created a model for services that are packed with modules and each modules has a price. Multiple modules create the price for that service.

- Service #1
-- Module 1 ($20)
-- Module 2 ($40)

Using belongsToMany

class Services extends Model
{
    public function modules()
    {
        return $this->belongsToMany('App\Services\Modules');
        ...

each module links to a price

class Modules extends Model
{
    public function price()
    {
        return $this->hasOne('App\Services\Pricing', 'product')->where('type', 'module');
        ...

and a service_module table that links services to modules. The problem is what kind of relationship should I create to be able to ->sum() the module prices for each service because I created an ugly patch with loops and burning 15 more queries per request

$prices = [];
foreach ($services->modules as $modules )
    $prices[] = $modules ->price['month'];
$price = number_format(collect($prices)->sum(), 2, '.', '');

via Chebli Mohamed