What's the cheapest back stretcher that actually works?

The plastic multi-level arch boards in the $15-30 range (ChiFit, MINOLL, and similar) draw thousands of reviews and serve as the entry point for most users. The trade-off is build quality and sometimes uncomfortable pressure on the spine. Reviewers across r/backpain and r/FabFitFun report meaningful daily relief from these inexpensive models, with the caveat that they're not built to last forever.