FabFilter

How much would it cost to upgrade from the Pro-C 2 to the Essentials bundle?

From experience I can tell you that it's roughly 19% off first plugin and 40% off 2nd.

So to add
Pro R is roughly $160
Pro Q 2 would be $107.

Total price for bundle with Pro C 2 sale is roughly $375.

It's always better to buy bundles as bundles FYI.

If you are a new customer I can send you a 10% off bundles as a referral.
Email me at jnwymore@juno.com if you want it. That would get your bundle to $360.