I went barebottom for the latest tank and while I wanted to protect the bottom glass from falling rock, I didn't care for the expense or bright white harshness of starboard. (The seafoam color might've worked, cost aside.)
So I came up with an alternative....
1) Obtain relatively inexpensive 1/4" Lucite from HD
2) Trim to fit using a metal cutting blade in a variable speed jig saw set on sloooow.
3) Throw a rough sanding pad on a random orbit sander and hit both sides. Gives it a nice frosted glass look.
Check it out...
Full tank shot from too far away...
(Pardon the lack of arrangement there - those rocks just went into the tank from being in a life support bucket for several weeks. I'll arrange them later.

)
The sheet was a 24x48 and was a little over $30. Thinner sheets are cheaper, but I wanted to protect the bottom glass as much as possible.
Anyways - I rather like the look and wanted to share.
Cheers!
Dan