Get an fishing rod, we can buy them here ( glass fiber) from 6 to 21 meters long, the last ones are made as vertical for ham radio peeps like us from several manufacturers, and come with guy wires and all.

But a fishhing rod alone should be a good start glass fiber and get a ground anchor for tents, or large sunshades, they come with hole to put the sunshade -pole in.

A bunch of alligator clips and wire, you have your pronto antenna...