I joined the package when tradewinds were offering an anniversary celebration discount, so that set me back around SGD370.
Once you are at Krabi, there are a lots of one day trip that you can explore. Each cost around THB1500 i.e. ~SGD65. You can go to the beach where "The Beach" was filmed, an island where one of the "James Bond" movie was filmed, or you can go trekking into the rainforest. These trips offers a lot of shooting chances
Even if there is rain, you can still choose to do rafting since you will be wet anyway ;p Otherwise, stay in door and enjoy a spa treatment, they are very CHEAP compared with SG!!