I was able to pick up 1 of each device from my local Micro Center for $16.66 each. In store they were both tagged as $49.50 but online they were $16.66. However they only had 1 of each or I would have got more. They had other stuff that was much cheaper online but I didn’t need them. Just go to microcenter.com and search for “Home Automation” and then sort by price lowest to highest. Get past the first page or two of switch plates and you might find some good deals. YMMV
GE Outdoor Module ($39.50 @Amazon)
GE Smart Switch ($34.50 @Amazon)
For example, this was $17 or $18 and it is $43 on Amazon. Not sure if this works with ST.