Good luck, I have no answers, but I understand where you are coming from.
I grabbed an Armasight Spark Core from Sportsman's Guide for $450 shipped, and as one of their club members I was able to split the $450 over four months. Made it easier to swallow. Picked up a Rhino and J-arm used, and an adapter on Amazon that was way cheaper and less bulky/complex than the Armasight adapter.
I'm pretty pleased so far.
My buddy had a Pulsar Challenger that I tried out side by side, brighter but less defined image than the Spark. He liked my Armasight so much better that he ordered one as well. I traded him a Seiko I no longer wear for his Pulsar and grabbed a used weapon mount off Amazon for around $30. I'll post some pics tomorrow of it mounted on an AR.
Both need IR illumination unless it's a bright moon or there is ambient lighting, but for under $500 it's probably the best you'll get for new helmet mounted monocular that didn't walk off a base somewhere.
I'm in the same boat, will be saving up for a PVS14 or maybe a Flir Breach thermal unit.
I'm a firm believer that something is better than nothing.