Mostly from local recyclers; also sometimes from folks on Craigslist who are looking to sell instead of recycle. Prices range dramatically based on the machine but $10 or less for a Windows XP machine is normal, $15-20 for a 4th-6th gen i3/i5, and it goes up from there.
I have relationships with a few recyclers and also volunteer my time with a nonprofit that also offers refurbishing; I frequently buy the machines they don't have time to deal with for low prices.
Recyclers have a huge advantage in getting their machines for free; I am too small-time to do that effectively. However, I take on the repair jobs they're not willing to do, so I get a pretty good deal on the inventory they have.
I have relationships with a few recyclers and also volunteer my time with a nonprofit that also offers refurbishing; I frequently buy the machines they don't have time to deal with for low prices.
Recyclers have a huge advantage in getting their machines for free; I am too small-time to do that effectively. However, I take on the repair jobs they're not willing to do, so I get a pretty good deal on the inventory they have.