Let us get this straight.
Admittance to Siam Park is ?32 non resident adult, ?21 non resident child under 12. All rides included.
Fast track one hour ?15, you can buy more hours.
The private log cabins are a VIP luxury at ?400 for 4 people maximimum for one day. I quote their website:
Private Cabanas (Phuket, Chaing Mai and Rataburi) for up to 4 people are available for hire during park opening hours for a really special day out. A cabana permits them to park entrance for 4 people, a private caba?a for the day, fast pass to all the attractions, Siam Park tubes and a limited all inclusive service including the menu in the Beach Bar, Beach Club, Thai Bar and Thai House Restaurants plus Water, Softdrinks, Beer and Wine.
Each cabana includes 4 sunbeds, a shower on the terrace, towels, fan, sofa, TV and a minibar with refreshments, beer and snacks.
It is case of you pay what you can afford but are assured of a great day out for your money. Try to go on change over days Tuesday or Friday.
This is the last I will post on this topic as I feel I have given as comprehensive an answer as I can!