The USD prices are the same here as on Steam, but since Steam converts to other currencies, you could see a difference in the converted prices. Since Steam can’t require external webshops to offer multiple currencies, this is fully in line with their policies. 🙂
You can purchase any packs on any platforms and once your accounts are linked they’ll be available on all. If you buy a pack here, they’ll be credited on your Steam account the same way as if they were purchased in their store.
As for the discount period – yes, the Digital Tabletop Fest just ended, but fear not, Halloween is just around the corner with the same discount. Just make sure you check back in the second part of the week. 😉