If you look online, you will find many people with low rates, and many (probably most) of them work remotely.
Our product engineers work on-site in our facility and within the frameworks of our company. Their managers look after the quality of the work. They have access to rapid prototyping equipment and testing equipment.
They also work within a larger team. They can tap our purchasers when they need to find sources for certain parts – not just to make a prototype, but also with the capability to make production batches. They can ask our process and manufacturing engineers to confirm the feasibility of certain designs.
All this translates into better work, fewer obstacles that slow a project down, and much lower risks of losing intellectual property.