Keep an eye out everywhere you can, deals do pop up. New with a warranty is preferred, but I understand sometimes that isn't an option.
I have less than $2000 in my two units. They may not be quite as good as a new TNVC unit, but at 1/3 of the cost, they're REALLY close, and as good as most of the brand-name units of similar type that I've compared to them to. No warranty and not knowing exactly what I have is the only downside.
The first, an Envis, was found on Craigslist of all places. The lady selling said several other locals had contacted her first, but wouldn't consider her $850 asking price when you could buy new Gen 1 ATN's for $500. She knew what she had, but had the wrong market. If you get an Envis, make sure the battery box isn't cracked, and remember that you'll spend $120 on the
adapter to helmet mount it.
The other is a PVS 14 I just got from a local gun shop I trust for $1000. I have no idea what tube is in it or if it's autogated, but for my use it is very serviceable. For that price, it's hard to go wrong.
That all being said, one of these days I WILL have a pair of TNVC Sentinels or Mod 3's with white phosphor. I made the mistake of putting on a pair. They're in a whole different league.