Firstly Thermal works day and night.
Presumably you want a spotter as opposed a mounted optic.
I would look at the NV section for some advice or speak to distributors like Thomas Jacks and ask them what you need to look for in any new or 2nd hand kit to meet your needs and the purpose you require the NV for.
Your use and the degree of sensitivity and range etc. will sort of dictate what is compliant with the job you need it to do.
2nd hand will of course make your money go further subject to Caveat Emptor and probably no warranty.
Leupold do or did a very small monocular style which retailed under the grand but it is a little crude in comparison with current stuff.
In a battle of wits I refuse to engage with an unarmed person.
To one shot one kill, you need to seek the S. Kill only comes from Skill