The smartthings hub doesn’t have any audio capabilities for the device itself.
Discussion here. 
It starts out discussing more expensive options and then gets down into the really cheap ones.
Also, if you can find a really cheap alarm clock which plugs in and continues beeping as soon as power is restored if the power was cut while it was previously beeping, you can just plug it into a smartthings-compatible pocket socket.
There are also cheap ($15 or less) power outage alarms which start beeping when power is cut. People usually use them to monitor freezers and stuff. Anyway, you can use one of those just as well – – plug it into a pocket socket and turn the power off when you want it to beep and turn them back on when you want it not to. It’s just a matter of finding a sound that you like.
https://www.amazon.com/Powerout-Power-Failure-Alarm-Safety/dp/B018A30T8Q
Although in order to really save money compared to the $49 aeon doorbell, you probably need to get an alarm clock at a local dollar store. Otherwise you’re paying $20 for the pocket socket and another 15 or 20 for the power failure alarm so you’re not really saving much.