right. So in this case, you could create tenats in supertokens as well and have user isolation there, but certain things like the jwt signing keys will be shared across all the tenants.
If you don't want shared keys across your apps, then you can create different apps in supertokens as well (and each app will have its own tenants), but this would require you to have different backends integrated with our backend SDK for each of the apps - cause the supertokens backend sdk is per app only.
Does this make sense?
About the pricing, we do volume based pricing (MAU + number of tenants). We would be happy to discuss this over a call:
https://supertokens.com/call-user