My “sleeping pad” cost $1 (some models are around $5) and can also be used for multiple purposes such as a wind blocker and as a heat reflector. It is a simple reflective window sunshade…the kind sold for vehicle dashboards to help keep the interior cool. It is flexible, folds like an accordion and can be rolled into a small lightweight bundle. (I’m barely over five feet tall, so one is enough for me; taller folks may want two for sleeping purposes.)
It can be used as an insulating sleeping pad, but it works even better when it is laid on top of a few inches of leaves, pine needles or grass to make a cushiony moisture-resistant foundation to put your sleeping bag on.
I pack more than one because it is a cheap multipurpose item. It can be made into quick wind block. It also makes a good heat reflector if it is hung in back of you when you or your shelter is in front of a campfire.