Any USB speaker would probably be fine. Even bluetooth speakers shoudl be fine. Then just run some alarm app and you’re good to go. You could make it more complicated by coding your own little alarm script, but if all you want is functionality, just install an app and be done with it. You could plug in a screen to set it up, but after that it would be easy to just have a headless pi sitting in a corner doing it’s thing. SSH in when you want to change something.

This is a project you should be able to finish in less than an hour. Maybe get a SDR antenna if you want to be a little retro.