The short answer
Priced per image or per project, driven by the number of views, exterior versus interior complexity and the level of realism.
Studios quote per image or as a project package. Exterior daylight views are usually the cheapest; interiors with detailed materials, furniture and lighting cost more, and animation or walkthroughs more still.
Budget for revisions and for good inputs: accurate drawings, material references and furniture choices. Most cost overruns in visualisation come from changing the design after the model is built.
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