For work I've got a several vizio smart tvs for digital signage. The smart part is worthless for this without a browser or android apps. They're on a mix of using usb drives and 15ish year old pcs for displaying jpeg slideshows. Just need a bunch of cheap devices to temporarily move away from those so they can be remotely managed (very very short staffed) while we wait on a full signage integration that is on back order.
Onn from Walmart. The 1080p "stick" is $15, the 4K "dongle" is $20. Both are good, the 4K is better, but not sure you would see any difference if the displays are 1080p or less.
Onn FHD stick is $15. THe UHD device is $20 but is larger and would have to be mounted with sticky tape or something. Other option would be an HDMI splitter with cables to each one, but that would probably cost more.
If they're Android (I'm confused from your post), you could just cast to them from any Android device. Temporarily at least.
The smart part is worthless for this without a browser or android apps.
I'm confused, do those TVs include a built-in browser?
Regardless, you can also try buying a bunch of Raspberry Pi Zero , Zero W , or Zero 2 W . The Zero series is extremely small, but still capable enough to run a Linux distro. The W versions have built-in Wi-Fi. The 2 series is newer, with better specs (but slightly higher price). They all include mini-HDMI port. I believe the price range is around $10 for the Zero W and $15 for the Zero 2 W.
Sure, the total cost will be slightly higher, because you will need HDMI cables (or adapters), USB cables, and MicroSD cards.
Do they all display the same image or different? If the first, then you can also look for adapters to just mirror one HDMI out to all of them.
onn 4k steam box at Walmart $20