I had the same thought about needing a generator and wanting a welder. I came across a very good deal on an almost new Bobcat welder($1497, 3 months old). I used to have to deal with rental property that required cleaning while empty(read no power). I figured 8kw and a welder would do it just fine. It did, but like all compromises, it has it's drawbacks.
One, the combination uses more fuel than a standalone generator, probably due to having all the extra mass that it needs to turn (?). I have never owned a 8KW generator, so I may be wrong on that. I just know that my little 4kw drinks alot less fuel, several times over.
I do know that the 4kw won't weld worth a flip, never has, never will.
If you don't use a standalone generator, it still requires you to start it up and run it or it won't start when you need it to. If you do enough welding to keep the welder in shape, that makes the backup a lot less trouble.
My problem began when I went over the road as a 18 wheeler driver, not being home to do the things I wanted, needing the welder less and the backup generator went with it.
I got an offer to buy it for $2000, so it went (after almost 15 years) and I purchased a generator for my lawnmower as a backup. I already had the buzzbox and an old Miller AC/DC/Tig machine, so that end was covered.
I only miss the Bobcat welder when I need to do something portable elsewhere and that doesn't happen very often, welding things I can't drag home.
All I am pointing out is, most of the options have drawbacks, and only you can determine which you are willing to settle for.
In the case of a power outage, the cost of fuel, hours on a tractor, etc are really trivial, compared to what the alternative is. Being able to get enough fuel might be a problem, but what it costs doesn't matter because you would pay twice that for it if you needed to. Being prepared for it also costs money, such a fuel storage that requires investment and treatment, and changing out to prevent fuel going bad.
I went with a 10kw generator for my lawnmower because it requires almost no upkeep, uses a fuel that I have a supply of (JD tractor tank is backup, 40gals, tractor trailer in driveway also a backup if absolutely required, 200 gals) and I use the buzzbox and Miller welder when I need them.
Just another point of view,
David from jax