If store bought lumber is difficult to acquire or too costly, a decent raised bed can be made by using smallish trees spiked together. Approx. 5" diameter in a double or triple stack log cabin rectangle is what I'll use. Easy to make with a chainsaw or even a battery powered Sawzall, can even be made with a bow saw if your gym is closed.
In a few years, when the bed rots, just push it in and build around it again. Probably wouldn't do that with pressure treated wood. Worms might rebel. Sticks, leaves, rotted wood in the bottom in a quasi hügelkultur will make the dirt go farther.
I'll be making two of those beds today, and placing them on a sunny bit of sloping land in a friends backyard where the best sun is on her most difficult terrain.