We sincerely recommend buying any second-hand Star TSP143 series with Ethernet (or entry model of Epson TM T20II with Ethernet), connect it via cable directly into the Wi-Fi router LAN, and use the tablet via Wi-Fi router to communicate with the printer like this.
An Ethernet printer may be connected via UTP cable in the network, (e.g. plugged-in directly in the LAN Wi-Fi router). When the order-taking device is connecting to the same Wi-Fi router (hence the same network) you should be able to see that printer and print with it.
IMPORTANT: Before you try this, make sure the thermal printer is correctly set (no lid open errors, load paper ok, etc) and properly connected to the Wi-Fi /LAN network, Bluetooth, or USB cable by following the manufacturer’s user guide instructions. Otherwise, the printer cannot be found during the auto-discovery search.
Moreover, for proper network/settings configuration, some printer models require a first-time setup using a PC and an installation CD coming inside the package. Make sure you’ve checked that before struggling with more advanced router IP settings.