BTW, he's probably doing this at around 1-3 labor points. I'm almost level 31, and I won't be able to start till level 34 and I am a pure builder too (just with one skill point in vigor that I haven't bothered to move back into construction yet - and didn't do the repairing quest and move that point either).
Once he gets to 10 or so labor, I think he should be getting over $300 per run at high motivation.
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High 'luck' jobs are way better than high cash jobs any day.
On my dueler on world 2, doing trasporting ammunition?
In around a total of 20 hours spread over 3-4 days,
Stone chain - sold for $500
Deringer - sold for $650'ish
Then,
Precise Muzzleloader - found this half way between level 27 and 28, right when I was trying to figure out how I could get one of them, since my town's gunsmith wasn't selling them.