If a Hellwin sold for $500 it either didn't work or was a knockoff. Others are far more knowledgeable, but I don't think there was more than one Hellwin model - it was or it wasn't, and they've been discontinued, so when you find one, they're pricey.
I'm sure Syn and Papa have a bunker full of 'em, but I'm also sure they ain't getting rid of them, so hunt and wait, and expect to pay in the neighborhood of $2k US, if memory serves.
For 90% of what a Hellwin is, you could get a 5150 Mk III, which is the architecture the Hellwin was modeled off of. Additionally, there are a lot of great real tube amps in many price ranges. There are a LOT of tube amp options that aren't discontinued, and new lunchbox tube amps pack a LOT of amazing features. I just got a PRS MT-15 which sounds killer and is louder than hell, and it's $650 brand new.