Take a look at the example in the docs.
I can't speak to the error you received as I don't know which line the error refers to from your example. In any case, the BlestaResponse is an object. You are looping over the object's properties rather than the package pricing you want.
// Fetch the packages
$api = new Api($url, $user, $key);
$model = "packages";
$method = "getAllPackagesByGroup";
$params = array('package_group_id'=>'2');
$response = $api->get($model, $method, $params);
// Output each package's pricing
if (($packages = $response->response())) {
foreach ($packages as $package) {
print_r($package->pricing);
}
}