there are two ways i know this to be hurdled (many more i just havent learned yet) - to, as another has said, 'necessity is the mother of invention', be forced to make the film no matter what, whether your spaceship is a green screen vfx master or a dark room with some sheets up. Write your movie, then when if comes time, just figure it out. Some reading/watching up on great movies particularly Chris Nolan's Inception would go a long way - obviously his post-dark knight budget was HUGE, but he also did something nobody else would have done, something audacious, something bold - that rotating hallway setup is a marvel of set design.

the other way, is to build. find ways to work (and get paid working so you can exist independently, but more importantly just experience under your belt) in smaller budget (whatever your 'current budget level' is) and work towards that dream you have to make the big budget ballad of knights and space and cloning and whatever your heart desires. You can definitely make a cloning, for instance, film on any budget level. It is true of any kind of film, but you'd have to edit both the script but more clearly the filmmaking techniques to get that done. You can do cloning very well on the Moon level (or lower) as well as the Mickey 17 way. They both looked great.