There is no avoiding the sand in those places, even 12 miles out to see there are sand storms. Natural sand is fine in a properly set up enclosure. I would avoid cacti, or at least choose spineless varieties. Cacti are new world plants, they are definitely not something a leo would naturally encounter and their spines could do some nasty damage to a leo's thin skin. There are plenty off other desert plants that could be used.
Desert grasses are, though
I was interested in setting up the same type of tank as well. This is what I ended up with: