Thermal, IR or image intensifier?
(Clarifying the difference between Thermal, intensifier and IR)
If you want 'cheap', you may find a cheap thermal or IR surplus Russian / Warsaw Pact gear from the late 80's / 90's. I saw both in Pakistan and Malaysia some years ago, for much less than you're expecting, all under $1K.
Rumor had it that some may have made their way to the US.
CAVEAT! Some of these were known to have a high UV output, and may cause long term eye problems (aka blindness).
Be careful if you go too cheap...
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.50 BMG: 1 Shot 1 THRILL!