Sell Add-On Services (Pro-Sites, Pretty Plugins)

Hey there,
is it possible to offer certain services or plugins on a month to month basis?
So for example:
User1 chose Plan1 for $10/mo and wants me to check security ($5/mo) and social media integration plugin ($1/mo). -> Total $16/mo.
It would be great if they could change llans and addons anytime.

Any way to realize this?
If not, this would be a suggestion that probably many users would love to see.

Regards from Germany,

Andy