Spend the money and get the tempered. All the others will scratch really easy and look terrible in a short time.
Do this, go to your local home repair center or window place, and get a small peice of plexi, lexan, acrylic, your choice. Take it home. Take the plastic off the glass and start wiping it aggressively with a wet rag, let it dry and sit out for a day or two, then do it again. Keep doing this for a weeks or so, and that is exactly how your shower will look in less than a few months, if you clean it regularly. Trust me, NOT pretty.
Do yourself a favor and go with the good stuff, you wont regret it. Im in the same boat, just got my quote for maple floors...