As far as sales, In the US they tend to be around the same times as other DIY projects. So if Home Depot is having a sale, you’ll probably see sales on home automation devices at multiple retailers.
We have a deals section in the forum where people post good deals that they see:
https://community.smartthings.com/c/devices-integrations/deals/
Some specialty retailers will also offer quantity deals.
There’s a list of retailers in the following thread: