I know filmmakers like to think they are making art, or their film will be different from all the thousands of others, but frankly films are not that. They are entertainment. Plain and simple. Consumed by the public like they consume food. Movies are no different.
Indie films are just cans of beans.
Thrillers have their place and price. Horror has its place and price. What you need is a sales agent to evaluate for you what your script, with the cast you think you can get for it, will do in the marketplace, what can be presold or other types of traditional financing accessed to make it, etc. The international sales agent will be your best bet. Once you are armed with this info, then you can start trying to get the cast, or if the film will cost more than the market will bear, shelve it and work on something that works economically.