You could buy a really nice rig for $2500. I love Sunn as much as the next guy, but to drop that kind of coin on a vintage rig that might need work and probably isn't doom-loud? I'd take an SVT-CL + 810 over that any day of the week.
Is at sexy-looking as a Sunn rig? No.
Will it level buildings and suffocate people in tar-thick low end? Hell yes.
Certainly, there are great rigs to be had at that price point. However, I think I come at it from a bit of a different angle. I'm not really looking to push massive lowend, otherwise I'd need to be looking at 300w minimum probably, so the 100w-200w range with efficient cabs is more useful to me as far as pushing the amps to the edge of dirt and really pushing the mids/low mids. Without the need to push so much lows, you cant get a bit louder before mush sets in.
I also have no hesitation as far as it being vintage gear that might need work. ANY gear will need work eventually, old or new, and barring the transformers, just about all of the guts are replaceable.
But if I were going for something with more lowend umph and power, I'd be looking at Hiwatts or their derivatives (HiTone, Reeves). I just have no love for Ampegs. I've tried SVTs a number of times, and they always just sound muffled to me. Even the SVT Heritage I tried. More power in the lows certainly, but felt the mids and highs were stifled. I'd like to try one through some of the 2000s cabs, I feel some of that muffle might be more in part due to the 8x10 fridge than the head. Actually, it's been a few years, maybe I should give the whole setup another go sometime.
@Turkeypills there's a 2000s on evil bay at the moment, a late '68 or early '69 from the looks of it, but it's a bit on the high side. If it were like...$1100-1200, it would be a pretty decent. There's also a few 1200s on Reverb, but again, a bit pricey.