$29 per month is crazy.
I'm Googling it and I'm not sure but I think all you need is to create a sound file, store it on a server and then code it into your html / listing. Once done, it would be free or whatever you pay for your server space.
Something to look into and educate oneself about.
Here is a link, and I'm looking at more. This is a music file but they have them for voice as well.
Adding background sound
Check this place out. Professionals record it for you.