Как добавить другую цену в корзину Opencart?

public function add() {
		$this->load->language('checkout/cart');
		$json = array();
		if (isset($this->request->post['product_id'])) {
			$product_id = (int)$this->request->post['product_id'];
		} else {
			$product_id = 0;
		}

		$this->load->model('catalog/product');

		$product_info = $this->model_catalog_product->getProduct($product_id);

		if ($product_info) {
			if (isset($this->request->post['quantity'])) {
				$quantity = (int)$this->request->post['quantity'];
			} else {
				$quantity = $product_info['minimum'] ? $product_info['minimum'] : 1;
			}

			if (isset($this->request->post['option'])) {
				$option = array_filter($this->request->post['option']);
			} else {
				$option = array();
			}

			$product_options = $this->model_catalog_product->getProductOptions($this->request->post['product_id']);

			foreach ($product_options as $product_option) {
				if ($product_option['required'] && empty($option[$product_option['product_option_id']])) {
					$json['error']['option'][$product_option['product_option_id']] = sprintf($this->language->get('error_required'), $product_option['name']);
				}
			}

			if (isset($this->request->post['recurring_id'])) {
				$recurring_id = $this->request->post['recurring_id'];
			} else {
				$recurring_id = 0;
			}

			$recurrings = $this->model_catalog_product->getProfiles($product_info['product_id']);

			if ($recurrings) {
				$recurring_ids = array();

				foreach ($recurrings as $recurring) {
					$recurring_ids[] = $recurring['recurring_id'];
				}

				if (!in_array($recurring_id, $recurring_ids)) {
					$json['error']['recurring'] = $this->language->get('error_recurring_required');
				}
			}

			if (!$json) {
				$this->cart->add($this->request->post['product_id'], $quantity, $option, $recurring_id);

				$json['success'] = sprintf($this->language->get('text_success'), $this->url->link('product/product', 'product_id=' . $this->request->post['product_id']), $product_info['name'], $this->url->link('checkout/cart'));

				unset($this->session->data['shipping_method']);
				unset($this->session->data['shipping_methods']);
				unset($this->session->data['payment_method']);
				unset($this->session->data['payment_methods']);

				// Totals
				$this->load->model('extension/extension');

				$total_data = array();
				$total = 0;
				$taxes = $this->cart->getTaxes();

				// Display prices
				if (($this->config->get('config_customer_price') && $this->customer->isLogged()) || !$this->config->get('config_customer_price')) {
					$sort_order = array();

					$results = $this->model_extension_extension->getExtensions('total');

					foreach ($results as $key => $value) {
						$sort_order[$key] = $this->config->get($value['code'] . '_sort_order');
					}

					array_multisort($sort_order, SORT_ASC, $results);

					foreach ($results as $result) {
						if ($this->config->get($result['code'] . '_status')) {
							$this->load->model('total/' . $result['code']);

							$this->{'model_total_' . $result['code']}->getTotal($total_data, $total, $taxes);
						}
					}

					$sort_order = array();

					foreach ($total_data as $key => $value) {
						$sort_order[$key] = $value['sort_order'];
					}

					array_multisort($sort_order, SORT_ASC, $total_data);
				}

				$json['total'] = sprintf($this->language->get('text_items'), $this->cart->countProducts() + (isset($this->session->data['vouchers']) ? count($this->session->data['vouchers']) : 0), $this->currency->format($total));
			} else {
				$json['redirect'] = str_replace('&', '&', $this->url->link('product/product', 'product_id=' . $this->request->post['product_id']));
			}
		}
		$this->response->addHeader('Content-Type: application/json');
		$this->response->setOutput(json_encode($json));
	}