I totally agree orb505, I've figured out what happened. Itch.io sets prices in USD and then autoconverts to other currencies.
On steam we set the price for other currencies, and we did that not realizing there was a difference. The itch.io discount was meant to be the same, as itch.io was essentially a release for our fans ahead of the game shipping on Steam.
If you PM me your paypal details i'll gladly refund the difference or the full game (and you can keep the copy), as I can assure you we value our early access players, and due to the way these systems set local prices caused this slight discrepancy.