3D Mesh Repair for Porsche 991 Model

I am seeking a specialist in 3D mesh repair and modeling to modify an existing Porsche 991 body shell STL file. The goal is to transform the current mesh (composed of separate components) into a single, unified, and perfectly watertight body shell ready for CNC milling and 3D printing.

The current STL file is composed of multiple parts (body, headlights, bumpers, spoilers, etc.). The required task involves:

Clean Separation of Accessories: Clearly identify and professionally separate all accessories (headlights, mirrors, bumpers, spoilers, etc.) so they remain distinct pieces for subsequent 3D printing.

Body Shell Assembly and Merging: Merge and assemble all core body components (roof, doors, fenders, etc.) into one monolithic shell.

Gap Filling and Sealing: Crucially, fill and close all gaps, openings, and junctions (created by the initial separation or the file's original architecture) to create a perfectly closed volume.

Technical Requirements (Maximum Mesh Quality)
To guarantee the quality required for CNC milling, the final deliverable must strictly meet the following criteria:

Watertight Mesh (Mandatory): The final body shell model must be validated as perfectly watertight (zero open edges, zero holes, and no non-manifold geometry).

Clean Topology: No inverted faces (flipped normals) and no internal self-intersections.

Output Format: The main deliverable should be the assembled and closed body shell as a .STL or .OBJ file.
Contractor Requirements
Please provide:

Your estimated cost for this technical service.

Your estimated delivery timeline.

A brief description of the software/tools you intend to use (e.g., MeshMixer, Netfabb, Blender, Fusion 360).