Turns out there is a built-in command in the Terminal utility-app on modern Macs that can be used for this. Launch Terminal, then at the command line, type:
>say -o outputfile.aiff "text"
and it will automatically generate an aiff file called outputfile, that contains an audio recording of your computer's text-to-speech voice speaking the text content within the quotes. You can select the computer voice in the system preferences, prior to running the script.