If you shop around you can find the metal raised beds reasonably priced. Or maybe cinder blocks if you have some laying around. The metal ones assemble quickly.

2x8”or 2x10” hemlock or similar are cheap and last reasonably long time. Especially if charred and treated with oil on the interior side.

I prefer corogated galvanized steel. They are lighter, easier to put together, move, and can last as long as many wood beds. You can find them dirty cheap on occasional sales at the usual getting spots.

I’ve seen Facebook posts for spare pavers and cinder block. These came with the property as junk. So a win win.