I’m thinking a bottlehead crack, darkvoice 336se, or a used massdrop Eddie current. I think you can get a Valhalla 2 around this range as well if you wanted schiit
The EC ZDT Jr, is very good, it’s actually a Laconic Night Blues with a different name, which you’ll find more references to or just LNB, but they haven’t dropped in a while so you’d have to pick up a used one I paid $250 for mine, I think it’s better than the Dark Voice at least with stock tubes.
If you buy the Crack you need to DIY it (or find one used), I understand it’s a pretty easy kit to build, you probably want the speedball mod for it, though you can add it afterwards.
I haven’t heard the Valhalla 2.
If you can still get one there is also a Russian guy on SBAF builds limited production tube amps called the Shortest Way 51 or SW51, that’s highly regarded over there and just fits in the budget if he’ll actually sell you one.
So personally I think the crack and ec are I think a higher tier but also different sounding. The crack is a very energetic and punchy amp going for an exiting tube sound (very tubey), where the eddie current is a bit more relaxed and going for refinement (it is OTL vs SET). The darkvoice is kinda in the middle, and offers a good balance for something tubey but not overly so. With these you can change the sound by changing the tubes
The schiit personally isn’t my first pick but yes it has a fair amount of the tube sound.