HCA: Hermit Crab Association

Hi! I have a variety of questions.
First, wondering where the best cheap place to buy sponges for water is? Or should I wait until I’m in Florida and buy some there? As well as shells, not super sure where to buy those either. Previously, I bought them from Amazon but there’s not a large variety. I have a pretty tight budget because I’m a student!
Second, my hermit crabs don’t seem to be using their pools? They avoid them at all costs, but maybe they use them when I’m not looking so I’m unsure.
That’s it! Thank you for reading.

Sponges for water dishes are not used anymore, as they harbor bacteria. As long as your crabs have a way to climb out of the pool that's all you need - some people put stones in the pools, or use little plastic ladders, or craft mesh/ plastic canvas.
I have ordered shells from Naples Sea Shells and Richards Sea Shells, when I had a US address.
If you have Purple Pinchers, they often just wade or toe-dip, rather than swim or submerge.