租车上的问题

在一个租车网站上看到下面这段话：


Book and pay by 15/07/11 for SUMMER and get 20% discount on basic rental!

Summer period applies for 15/08/11- 15/03/12. Only applies for website Bookings. We will refund your 20% basic rental when you come to pick up the car.


我看中了Touring Cars

Nissan Bluebird or Similar $37

Vehicle Features Nissan Bluebird or Similar 1800cc - 2000cc manual/auto Radio / Cassette Player, Optional CD Player / Cell Phone. Daily rate includes GST (NZ sales tax), unlimited kilometres, std insurance ($1,500 excess) and 24 hr AA roadside assistance. Power steering, Air con.


准备今年底明年初的那段时间租来环南岛一圈，大概3000公里，3个成人乘坐，2个大拉杆箱+1个中拉杆箱。网站的预定系统算下来租16天是37*16=555元。是不是意思说，在555元的基础上打折，在我提车的时候退换我20%的租金？是要在7月15日前完成预定并把钱先付给这家公司吗？请专家来帮我们看看是否划算？谢谢！