I use an Aeron; I actually found this one for free, but in the past I've bought used for $250-350. I did actually buy a new aeron once, and then had it air-freighted for $300...and it was entirely worthwhile, sitting in it 15h/day, 7 days a week, for a year or two, and then selling it for the price I paid.

(relatively inexpensive) capital goods like chairs, good IPS LCD panels (3 x 24, or 1 x 30), laptops, etc. I'm quite comfortable spending money on, as long as I need them, and get a great price -- it's really only consumables and recurring costs I try to minimize whenever possible. And even there, I am more than 5-10x as good at bringing in revenue when I have $5-25 meals vs. ramen or beans, so false economy is false.