Why is there such a huge price range for BNC terminators?
For BNC terminators there are usually the following factors that contribute to the price:


Accuracy of the specified values (i.e. impedance is matching for the whole assembly)
Wattage of the resistor
Bandwidth of the whole assembly
Linearity of attenuation of the whole assembly
Contact quality


Some of these have similar influences to all kind of other BNC equipment too