I'll toss in a few different options, some of which already have been suggested.
If you're looking for a really inexpensive Neck knife you could go with the a Livesay. However, if you spend a few more bucks you can get a great knife that is more refined from Allen Blade (the Chipmunk). Also, Allen's Kydex sheaths are much better than Newt's. For a while Allen made all the Kydex sheaths for T.O.P.S. knives.
Finally, if you a knife over $100 isn't out of the question you could get a Dozier Razorback Neck knife from Knife Art. Wonderful knife for the money, D2 Steel, great blade design and superb Kydex sheath.
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Marine Sniper Motto:
There's no use Running, you'll only Die Tired!