I am getting conflicting points of view on the proper foundation for an air mattress. currently I own a nice bed frame that calls for a mattress and box spring. I have been told by the manufacture that I need as close to a flat surface as possible, this signals some sort of wood slat or wire mesh system. Are there any box springs that would fit the bill without costing 300 or more for a king size? I am also toying with the idea of getting the cheapest possible box springs then laying plywood or bunkie board on top. any help would be great as I am trying to stay within a tight budget.
Hi Kesco,
Welcome to the Mattress Forum! 
You’re correct that most air mattress manufacturers will request that their product be placed upon as firm and flat of a surface as possible. Solid decks are quite popular, as the closely spaced slatted networks, and sometimes even a metal grid (sometimes referred to as semi-flex or min-flex grid).
The foundation thread here has links to a multitude of sources for various non-flexing foundations, including some low-cost alternatives.
Your thought about using some sort of a foundation and then placing plywood or bunkie boards on top of it can also work, provided the foundation you purchase had enough basic structural integrity to allow for the support of the plywood or Bunkie board.
If you have any other more specific questions, let me know and I’ll do my best to provide more directed answers.
Phoenix