If you only need four buttons, you can use a Wi-Fi phone. You can typically get those at Walmart for right around $20, but there are even a couple you can get from Amazon for about $25. You just don’t activate the calling plan. 
The Aeon wallmote is also worth considering, except the battery life seems to suck. So you might get need to get creative on that part.
https://www.amazon.com/Aeotec-Aeon-Labs-ZW130-WallMote/dp/B01NCEJAOD
The Lutron pico 4 button controller is perfect once you have it set up. Battery-operated, but it’s a 10 year battery, and each individual device is cheap. The problem with that one is that it doesn’t work with the official SmartThings integration, so you have to set up another device like a laptop or a raspberry pi as a "man in the middle. So once you have it set up, it’s a nice button, but the set up is a lot of work. Still, if you need a bunch of them, even with the extra server it’s probably cheaper than the Leviton’s.
Just be aware that this option has a fairly complex technical set up requirement.