Higher-end DSLR bodies cost more for a few main reasons:

1. Larger sensor: The Nikon D700 uses a full-frame (FX) sensor, which is significantly larger than APS-C/DX sensors. Larger sensors are more expensive to manufacture because fewer fit on a wafer and defects waste more chips.

2. Pro-level body construction and features: Cameras like the D700 are built to a higher standard, with features such as a more robust chassis, more direct external controls, and support for older AI lenses with metering.

3. Professional support expectations: Pro-grade cameras often carry added costs for better service infrastructure, such as parts availability, faster repairs, replacement equipment, and support staff.

4. Market positioning: Premium models are also priced higher because buyers in that segment are willing to pay more. In practice, flagship and pro bodies often carry a disproportionate premium compared with entry-level cameras.

So for a model like the D700, the biggest technical price jump is the full-frame sensor, with additional cost coming from build quality, feature set, support, and market positioning.