Based on my research the best budget-friendly option is the FLIR Scout series. They aren't "night vision" per se but they are thermal, which has some good benefits over starlight/night vision for /out/ (i.e. they aren't great for seeing through windows but they're superior for IDing warm bodies despite foliage, weather, fog, camouflage, etc. Also it's not just a monocular, but also a camera that can take stills and video.
This cheep model has a detection range of >100 yards and 8 different colour schemes that each work best in different scenarios. I just bought one but it hasn't arrived yet.
https://youtu.be/-h5CRhyvJo8 