As some of you may know, I have a fairly extensive yoyo collection.
One of the challenges with having a large collection, however, is where to put them all! Before I post my suggestion, I'd like to note that probably the best and most attractive cases I've encountered are the ones that Brett Grimes makes. They're very reasonably priced, especially considered the minimal shipping charges, look great and do a fantastic job of protecting yoyos. If you're looking for a great case to store under 21 yoyos or less, I would suggest you check them out.
However, if you're looking for a very economical way to store
a lot of yoyos, you need a case option that is really cheap. After searching nearly every fishing tackle, super store, crafts store, etc., I have finally settled on what I believe is the ideal 'cheapo' case. Presenting the: Sears Stack_On 14-1/2" 17 Compartment Storage Box - Red. (Sexy name, no?) This is a great storage solution. Here's why:
1. The compartments are perfect fits for most yoyos.
2. The lid is clear so you can see inside.
3. It holds 24 yoyos. (You may need to use a bit of foam or cardboard to divide some of the 'double wide' compartments, however.)
4. It stacks on top of itself.
5. It's readily available at Sears.
6. It's cheap! $6.99 regular price.
Here's the Sears Item# 00962314000 and the Model# SBR-18.
And a few photos of the case:



I have about 10 of these cases filled with yoyos (and another four or five of Brett's cases I think). If you've been looking for a great 'mass storage' yoyo case option, hopefully this helps you out!