In the ol' days, we used to get a used inner tube, patch it up for pennies, get some line to wrap around it, and a burlap sack to wrap into the inner tube float. Good quality nylon line is about $3, an inner tube may be free if you look hard enough (tire stores, may need a patch kit), and just about any sack will due. If the sack is deep enough, you can take the end and move it around the tube, up and over, and into the inner area for travel. Get a floating dive line to tie the float to either you or an anchor, and a dive flag for the float, with a wooden dowel to tie the flag to. An older-style camping air mattress would also work. Use you brain, and explore the types of floats you could build.
SeaRat