China Imperial diesel I have experience with, they are the cheapest of the larger suitable to power a home model units I have seen (as in multiple cylinders, you ain't picking one up). Wouldn't call it real portable unless it was mounted like the one I maintained inside an old van. Cranked and ran perfect all the time.
With that said, the cheapest way to get a decent genny is to buy one with a used RV wrapped around it. I ain't kidding, you can get fair used but still functional RVs for around 1500 bucks with a genny in them, plus large fuel storage tanks, extra stored water if ya want, built in this or that, usually propane tanks along with the liquid fuel tanks, little furnace, another AC unit. Ours only cost one grand even, got it from folks who upgraded units and it was sitting in the ratrow in the back of the RV park. All it took was a good cleaning and that was it, vroom drove it out, lived in it almost five years. You couldn't buy the genny in the thing outright for that. It's a gasser though, with a kohler engine and a separate fuel tank, but it wouldn't take much to tap into the big main fuel tank either.
Most houses have a building code, check local and with fine print in insurance, they will give you grief if caught holding more than 25 gallons gas or diesel in plastic fuel jugs, but...you could have two hundred gallons in an RV with dual big tanks and they wouldn't bat an eye. and installation couldn't be easier, heh. You could do the same with a ratted out cheap but still running diesel truck with dual tanks plus a bed tank and a diesel genny mounted in the bed. That's the easiest way to store, haul, refill things on a large scale.
Just a unit, and if ya want diesel, used at RV junkyards or marine junkyards, pickup all the electronic doo dads that go with it (that's the stuff that adds up quick in cost with generators). My current boss's rv (cost more than most folks houses, think rockstar class RV) has a big diesel genny in it.
OK, with all that crap said, there's a ton of cheap diesel gennys online. I was looking at some last week just internet window shopping. I have zero experience with them, but the same chinese diesels, small single cylinder on up, are in use all over the third world planet and they run, and guys have used them to repower this or that device, (garden tractor, water pump, and etc.,) and have found they run OK and are real fuel miserly.
In the alt energy community they seem to have been received well, small homeowner gas gennies, not so much, they don't last long at all. Talking about folks who actually live off grid so they can't fool around with crap that doesn't work. A common offgrid setup is solar and or wind plus genny plus battery bank and charger/inverter setup. This is called a hybrid system, and is by far and away the most common type of alt energy setup most folks have.
Home Power (dot com) magazine is *the* go-to place for real info on this subject of powering your home/building/whatever off the grid. They have an online site as well as their paper magazine. That and mother earth news.
: 
