What kind of lizards are they? I have drilled holes into logs for my ackie, he can't get enough of them. Or you could find some hollow branches/logs? Natural looks best
PVC pipe cut in half and covered in grout is the easiest option as mentioned by sawowie.
If humidity wasn't a problem and you wanted a larger hide you could always paper mache a ballon, wait for it to dry, pop the balloon, cut in half, hide
If you wanted to waterproof it, you could cover it in grout or paint it with pond sealer.