Sort by price

i can see this but don’t know how to switch to price

<?php 

									// Order by date url
									$order_date = isset( $_GET['order-date'] ) ? esc_attr( $_GET['order-date'] ) : '';

									if( isset( $order_date ) && $order_date == 'asc' ) {
										$date = 'desc';
									}elseif( isset( $order_date ) && $order_date == 'desc' ) {
										$date = 'asc';
									}else{
										$date = 'asc';
									}

									// Order by price url
									$order_price = isset( $_GET['order-price'] ) ? esc_attr( $_GET['order-price'] ) : '';

									if( isset( $order_price ) && $order_price == 'asc' ) {
										$price = 'desc';
									}elseif( isset( $order_price ) && $order_price == 'desc' ) {
										$price = 'asc';
									}else{
										$price = 'asc';
									}
								?>

Any advice on this please