4 Therm-a-Rest Ridgerest ground pads. The gold standard in foam sleeping pads. I spent many years camping with these, finally upgraded to something expensive. Insulating and comfortable. It's not an air mattress, but it's $5.

https://www.backcountry.com/therm-a-rest-ridgerest-classic-sleeping-pad

I have 4, see the picture. From left to right:

1. Regular 6', great condition. $15
2. Regular 6', black, fair condition -- one large tear. $5
3. Regular 6', good condition -- one small tear. $10
4. Small 4', great condition. $8

We can meet somewhere at Stanford. Cheers!

Tags: sleeping pad camping backpacking groundpad mattress