What is the use case? It's a paid actor, why do You need to give it for free?)
There is trial period, when user can test your actor for free. Otherwise, You can give the codebase to the user => he can build the actor under his account and use it for free.
Suppose, I want to invite user/devs to test it(for quality control) but say one may not want to share the entire codebase(for security reasons), how can we proceed in this situation.
No smooth /straightforward solution in this case, I guess. He can make a build from your private repo. You'd just need to add his deploy key to your repo. He won't see any code and can use your actor.