I think an important part of your friend's statement is "could" cost.
Increased price can imply rarity and reduce the number of sources as to where such a knife could be obtained. This, in turn, could make local purchases easier to track.
And now, the "could"... Many knives in general, and Ka Bar / Ka Bar like knives in particular can be said to have four general levels:
1. Inexpensive knock off
2. Mid range production
3. Higher end production (usually better fit / finish and better steel than the mid range model. As with say, woman's purses, slapping a prestige brand name on it also increases the cost).
4. Custom made by a knife smith.
In referencing say, the $300.00 possibility, your friend was probably referring to level 3. Purchases of these would be slightly easier to trace as there are fewer manufacturers and also fewer purchasers.
But.... there are alot of mid range Ka Bars, including the Ka Bar by Ka Bar variant going for $90.00. I imagine that there would be far more purchasers and thus harder to track.