Mechanical Design Engineer: 4-color retractable pen mechanism (3D-printed prototype)

I’m developing a larger-than-normal version of the classic BIC 4-colour pen and need a functional prototype for further development. The job is to take my detailed specs (spring rates, hole sizes, tolerance... (Budget: $30 - $250 USD, Jobs: 3D CAD, 3D Design, 3D Modelling, 3D Printing, 3D Rendering, Manufacturing Design, Mechanical Design, Mechanical Engineering, Product Design, Prototyping)