If you're not too psyched about weight the already suggested Peavey Mark heads (even the least powerful Mark III -my 1st. serious amp- is real LOUD) can be had for 200$ or less. I've also owned both the old MOSFET Hartke 3500 and currently own a later non-MOSFET one, they both punch and are equally as capable, versatile, reliable, and loud (even run at 2.7ohm, did it for years, hit the head's thermal protection probably twice in 30 years of Hartke gear) and can be had for <200$ too.
There's 2 class-D heads I'd buy under 500$, one is the Peavey MiniMAX (or a used MiniMega) and the other is the Tech21 VT-Bass 500 (probably my fave, my rig for the last 10 years has been a SansAmp RBI thru' the aforementioned 3500 head, I've been in love with the SansAmp thing for 20+ years, only comparable thing to ever come out being DarkGlass IMHO). I've tried others, Tone Hammers several times, and I don't like them, hardly plug&play, always DIFFICULT for me to find a tone I like, also no blend for fine tunning the overdriven thing (which on top of that I find really lame sounding, guitar-like, no grain), and it doesn't seem to punch like solid state heads usually do, kinda' dull. I know MANY love Tone Hammers, so I asume it must be my SansAmp fat crunch (mostly picked) punk/metal bias. I also tried an EICH T500 but can't say for sure as it was thru' their 1x10" and 1x12" cabs which I find laughable at best (really thin sounding, wouldn't even use those at home, what an expensive joke). It all sounded too "flat" for me, no punch, no balls, no chest pumping part of the spectrum, even at low volumes (and wasn't even trying to punk that head at all, playing mostly tasty disco/soul/funk fingerstyle Bernard'ish stuff). Contrary to some trends I happen to love voicing, couldn't care less for "flat", this is about amplifying bass guitar, not the RPO.
What I've been doing for the last decade+ is carry my tone with me either in the RBI or its emulation in a Zoom MS60B, so I can use any amp that puts out enough clean volume and has capable enough EQ to adapt to the room (kill resonances mostly), even any of my cheap jewels (an array of Peavey combos). That's why I've been doing good exclusively with Peavey and Hartke gear (loud and reliable), never owned anything else (same with cabs), loud (while clean) and with a versatile enough EQ is good enough for me.