Gumlet looks like a good option if you can stay within the free plan.
I just checked out my SoundCloud account to get an idea of the number of recorded minutes I have, to get an idea of what the limits imply.
In total I have over 250minutes of recording already, which is above the free limit on gumlet. This includes multiple recordings of the same piece using different virtual pianos so not perhaps representative.
I have a playlist of all the songs I have recorded with just my favourite recording of each song and that is 197 minutes.
For me anyway it does feel like the sproutvideo seed option at $10USD a month is the best choice. But I was quite tempted by gumlet.
If you choose to try gumlet let us know how you get on Marie.