The Math Ring

This Sterling Multi-Gemstone Set of 5 Stack Rings for a mere $49.99, which comes out to just under $10 per ring.

And you can wear this ring numerous ways - just a single ring (5 different color combinations), 2 rings together (10 color combinations), 3 rings together (10 color combinations), 4 rings together (5 color combinations), or 5 rings together (1 color combination).

If you want to get into the unique permutations, go ahead - I just figured out the color combinations and I feel geeky enough.

Anyway - with just color combinations alone, you can have 31 unique color combos (which comes out to roughly $1.61 per color combination)!