I'm the lead architect of an architectural studio/practice experienced in architectural design, construction drawings, project management, construction site supervision and outsourcing solutions for the architectural domain (drafting, 3D modeling, visualizations, Photoshop editing, presentations etc.). We form a team of skilled professionals with proficiency in several specialized programs: ArchiCAD, AutoCAD, Revit, SketchUP, 3dsMax, Cinema 4D, Photoshop, Corel etc.
We have similar experience with other individual architects / firms (like yourself) were we provide 3D modeling and renderings from hand sketches, 2D plans and elevations, conceptual drawings etc.
I would say that we agree with your prices / terms but just for the first project. Unless you have identical projects (scale and detail levels) the same price can't be applied to all future projects. A much more accurate way would be to appreciate per project the amount of work (easy to d when you've done a couple) and to negotiate a price for that specific project.