Maybe it's a usage thing--more sales in 120 vs 35mm? There seems to be a similar but slightly smaller gap in prices here across the pond.

35mm would be somewhat more expensive to make (metal canister, 2 metal end caps, perforation), and the base material is thicker, perhaps a little more expensive, but this doesn't seem to justify the differences I'm seeing. But if 35mm users have mostly abandonded slide film and 120 users haven't, then lower volume could easily account for the difference.

Charlie Strack