Is there an easy and inexpensive way to add privacy to a screen tent?

Answer 1

put a tarp over it.
It will get hot so make sure you leave a space at the top.
Another thing you can do is to simply take some clothespins and pin it up.

you could pin a blanket around it or a bed sheet. Or drape either across the top

Answer 2

throw a cover over it with a hole at top