Recommendations for WiFi access point?

I'm helping a local organization with some wifi issues. They are currently using a Linksys RE6500 WiFi extender. The router is 50' away from the extender and there are 3 concrete walls between the two. When connecting to the WiFi extender it frequently cuts out.

I'm looking for a better access point that I can run a 50' Cat5e ethernet cable to. What should I look at getting? I've read Google WiFi is a good solution. What else should I look?

The connection may have 10-15 devices connected at a time.

Thanks for the advice in advance.