Sound Gone on Macbook Pro Retina 15" late 2014 running MacOS Big Sur 11.3 Beta

A few weeks ago, the sound on my Mac just died. Nothing was coming from the internal speakers, the headsets, or external systems. When I get into the sound icon from system preferences, I'm told that there are no input or output devices available. Everything but the sound works fine, except if there's an interview in a story, music, or any audio, I get dead silence. Is this a fatal breakdown or can it be fixed for under the $2300 I paid for it originally? I didn't expect it to help, but I tried to restore everything with the Time Machine--no luck there. Thanks.