There’s no single answer as it depends on what type of wood and other materials you want to use; however, here are some general steps you can take to reduce costs while still getting good results.
You could try using plywood instead of hardwoods (like oak); buy your lumber from Home Depot rather than building sites like Lowe’s etc.; look at buying pre-finished furniture pieces/mullions (that is, finished slats with a thin veneer over them) instead of having to finish everything yourself; consider buying premade “platforms” (bed bases made up of multiple boards glued together). If you don’t know which option best suits you then ask someone who does because this kind of stuff isn’t usually covered by warranties.
You may also find that if you’re doing most of the work yourself then you’ll spend less overall. For example, many people tend to underestimate just how much time goes into cutting, fitting, finishing, sanding, painting, etc., when working alone. So, if you plan to build more than 1 bed base per year then maybe hiring an experienced carpenter would help (or perhaps two or three carpenters?). Also think about whether you’d prefer to start out small, e.g., by starting with a twin-sized mattress first, before moving on to larger sizes later. This saves money initially since you won’t need to pay extra for large mattresses vs. smaller ones. When you get started though, remember that cost savings aren’t always worth sacrificing quality — especially given that you might not realize it until after completion.
What you really wanted was cheap, easy, fast, and sturdy. The simplest method is to order individual slats, rails, headboards, footboards, and possibly corner posts. Then simply assemble the various parts together. You can buy a set of 8′ long slat legs from Sears for under $5 apiece. These slats fit perfectly and gave excellent support. Another benefit is that the dimensions allow the slats to sit side-by-side when assembling, thus saving valuable floor space.
Another possibility is to use precut panels. Many manufacturers produce complete panel sets consisting of 3′, 6′, 9′, 12′, 18′, and 24′ wide sections, along with matching tops. Most of these panels feature dovetail joints, meaning that they interlock directly without needing any additional tools or skills. Of course, you’ll probably want to consult the instructions that came with your particular kit.
Finally, there are a lot of kits available where the manufacturer sells separate elements such as slats, rails, posts, etc. All you need to add is the top. These are typically more complex due to the number of different elements involved. However, they provide greater flexibility since users can mix and match pieces according to personal taste.