You can even use an ESP32 or similar since it just has to perform 1 tiny function.
Getting an WT32-ETH01 knockoff dev board for 15€ or PoE for 25€ and uses <300mW with the wireless modem off. You could even just use a WiFi module for 8€ if you don't want something wired.
https://registry.platformio.org/libraries/a7md0/WakeOnLan
There is already an wakeonlan library to generate a packet very easily.
You can even do it in pseudocode with ESPHome if you have HomeAssistant
Then VPN in, send a signal to the esp using one of various methods to tell it to send the packet.