Surgical Drill STL-to-STEP Conversion

I have an existing surgical drill device captured only as a high-resolution STL mesh. I now need a clean, fully watertight solid model in STEP format so the part can move straight into CNC machining and other manufacturing workflows... (Budget: ₹12500 - ₹37500 INR, Jobs: 3D CAD, 3D Modelling, CAD / SolidWorks, CAD/CAM, Mechanical Engineering, Reverse Engineering, Siemens NX, Solidworks)