I don't restore cases. If you get one of my instruments and don't like the old case, ProTec cases offer good protection, and are a great value. You'll find them easily on the Internet.
Cheaper Chinese soft-sided and hard sided cases are readily available on the Internet and are a great value at only $30-35. The soft-sided cases offer good protection, but the drawback is that the zippers will fail in a couple of years. This one from Hyson Music is very sturdy and will last longer than the soft-sided cases.
There are other options other than standard cases. I used a Martha Stewart silverware holder to make a serviceable case insert. This makes it easy for me to carry penny whistles, folk flutes, and recorders, in addition to my clarinet— all in an old computer briefcase.
I cut the spoon part off. But that part is useful for keeping the bell.
Long draw string bags keep the clarinet sections from bouncing around too much.
I think many students would be interested in carrying their clarinets in their school backpack. My silverware holder works well if the backpack has a section for a laptop.
Bells and barrels are very sturdy. Just slipping them in a separate bag is protection enough.
A backpack with a clarinet in it MUST NOT BE DROPPED from the shoulders to the floor! Treat the backpack as you would if it held a computer.
Another option are various tackle boxes and craft boxes.
I use a zippered ‘digital media container’ to hold my mouthpiece and reeds.
These thin tackle boxes would fit very nicely in a school backpack. But the bell has to be put in a separate place. See more on this below.
Note that it is best to put the two keyed joints in protective bags or old socks. Wrapping the two keyed joints in a wash cloth will also work.
Here's another $5 tackle box option I like very much. Again, this would work great to carry inside a school backpack.
As I said above, clarinet bells are not fragile. If your bell is wooden, please try not to drop it. The bell can be put in a bag and slipped in an extra pocket of your backpack.
There is an alternate bell that will actually fit in this tackle box! See The Backpackable Bell here.
For cleaning out moisture, a chop stick can be used to push a handkerchief through the individual pieces. It is best not to store the wet cloth inside the clarinet case. You want the cloth to dry out!