Only thing that will consistently positive ID at that range is high end magnified and illuminated get 3 NV. You're talking 3-5K for something that'll do that. Now if you're wanting something cheap get a Sightmark Photon XT plus a decent illuminator and then call them in a little closer. You should be able to see them pretty good at 200 or so with a good illuminator.
Thermal is great for detection but you have to be very experienced with it to positively ID critters at those range. And that's with high end 640 units and even then a positive ID with thermal at that range is difficult.
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