Going through my craigslist offerings here. I see a package deal on Ampeg SVT 3 Pro bass rack amp, with a DOD 431 series EQ rack mount, with a Korg DTR-2 rack mount tuner for $500, but the amp weighs like 26lbs or so.
Thats not that bad, I have a tube head that weighs 97 pounds. Its not a terrible price if the rack is included.
Thats a pretty good price for an amp, I might jump on that deal. As far as minimum impedance goes, the vast majority of amps are only safe down to 4 Ohms. I would only be looking at smaller cabs that are 8 Ohms, or bigger cabs that are 4.There is a GK MB500 for $300, seems alright, but the specs say it only can go down to 4 ohms.
I guess another question would be if there is any good lightweight power amps in an affordable range. Supposing I have a decent preamp going into it, perhaps a line 6 bass pro xt or what not.
You can go this route, just be sure to check that your pre amps output is suitable for your power amps sensitivity. The other thing to consider is that this isnt going to save you much weight once you add in a rack to house everything in. That said I use a Peavey IPR 1600 in one set up. 7 pound amp, 1600 watts of power.