How do you build a fantasy world?

[Kelly Goden]

Building sets in cg isnt hugely difficult, there are training resources like digital tutors that show how to make realistic environments. But you need a good deal of traditional artistic skill and knowledge in addition to learning the software to make it and the lighting look realistic(unless you went for a stylized environment).

If you dont plan much camera movement in shots where you have the fantasy sets(like a pre Steadicam era movie) you would have much wider options for altering the backgrounds.

You could build partial sets--just enough to cover the performers in shots, and then paint in the rest digitally. You could do a lot with photoshop or after effects. Would require careful storyboarding and planning, matching lighting etc.

Depending on how ambitious your script is, to do what you want in a respectable way doesnt require a huge amount of money, especially with the technology available now, but it does require a great deal of artistic skill. If you cant DIY then getting it as cheap and yet as good as possible becomes the issue.
Maybe you could commission someone to build an adjustable model(s) that they get to keep and sell, but you can use for your film.

You might be able to arrange something similar with a freelance digital artist or ten, since you can find them anywhere in the world.

Personally, for something in a fantasy setting, the less cg it looks, the better.
Even on big productions they still use miniatures frequently.

Its just more convenient than building it all cg.