What is the difference between cheap and expensive GPS receivers?
See How many GPS channels make sense?

That long answer details how adding more channels to a reciever (at additional cost) can:


Speeds up satellite acquisition
Reduces power consumption
Reduces likelihood of losing a 3D fix even in urban canyons
Provide better sensitivity, allowing fixes in dense forests, and even in some tunnels
Provides better positioning accuracy


Edit: channels are one factor. A big factor seems to be the fiber-optic gyros in those other units; those are something I can't even find pricing for on the internet. But really I suspect a lot of the costs for the professional kit are non-recurring expense (NRE) of various sorts. More complex software, especially for sensor fusion. Proprietary position-enhancement techniques. Certification and compliance (I see "export compliance" on one of those feature lists, maybe there's a legal cost associated with that?)

High NRE divided across small number of units sold = very high unit cost for seemingly modest performance improvements. Not unusual when dealing with lab or test equipment.