FAQ: When ordering a Dolphin unlimited license, will there be any additional fees?

You will have free access to all new Dolphin versions, but you will almost certainly want to customize your site, which may require additional investments.
Should you need any additional functionality beyond the Dolphin default script, you will need to have it customized or you can check on the Unity Market where independent experts offer their mods and services.

At any rate, Dolphin is open source, and you are free to do any customization you want/need.