We use the existing standard for the WiFi access point.
We have had good experiences with the FritzBox 4020 (under 50 EUR). However, an older (used) Fritzbox works just as well. However, these usually boot significantly slower.
Experiments with RaspberryPI with OpenWRT did not satisfy us and even turned out more expensive than the FritzBox 4020.
Experiments with FritzBox 7170 showed that after uploading config files, it got tangled in UDP communication. The status of the modules turned red. Only disconnecting the PC from the model railway WLAN and reconnecting it brought the system back to life. With a (newer) FritzBox 3272, however, this problem did not occur.