I guess the question then is whether there's a market for 48kbps opus music. But that'd be assuming that a big part of the costs are bandwidth. I'd bet that's not the case.
Also imagine how little traction you'd get once people associate your brand with poor music quality. I don't think you can compete by being 2€/month cheaper.
If you control the client and are able to update it, I think you're better off switching to opus or similar.
96kbps opus is actually quite good for music already: https://wiki.hydrogenaud.io/index.php?title=Opus#Music_encod...
I guess the question then is whether there's a market for 48kbps opus music. But that'd be assuming that a big part of the costs are bandwidth. I'd bet that's not the case.
Also imagine how little traction you'd get once people associate your brand with poor music quality. I don't think you can compete by being 2€/month cheaper.