You would probably need to develop a custom App that manages the Payment.
You can restrict Apps to certain User Groups.
The custom App would need to track wich users have paid and what membership they have and then put them into the right group/groups. The extra Storage Space would need to set by the App too (i dont think that can be done with groups).
How would Customers pay ?
If they have to be able to pay digitally it might be pretty complicated to implement.
You could also do the Accounting manually and have a person track the payments (wich only works up to a certain amout of paying users) and put them into the right groups.
Nextcloud is extremely felxible and this is definitly possible, but it might be a lot of work.
To my knowdlege theres no public App for this yet, but some business might already have developed a closed source solution to this.
Generally i think the best idea ist to contact the Nextcloud Gmbh and ask them. This is probably not the first time they had a customer asking for this.