I used 5 pallets and some wood scraps to make these two and that part was free. If you want to paint or add cushions (recommended!) that will be extra but all in all this cost me $10 for the red paint and that's it!
The basic idea of how to make these is to take two pallets of the same rectangular shape and stack them on top of each other, do the same with the second lounge chair. Then take the last pallet, divide it in half and add some wood scraps to construct two backrests that you attach to the stacked pallets with two screws. Minimal sanding and some paint and you're done.
I must warn you that the idea is simple but deconstructing the 5th pallet is pretty hard physical work but can be made easier if you have the proper tools and/or a muscular guy to help :)
Check out my blog for more photos and detailed instructions on how I went about it: