1%? I'd say more .01%.
Well, it depends on his budget, and what equipment he had already. If you have unlimited money, you can build a fusor straight from a Cole-Parmer catalog.
Buy a vacuum chamber, bolt a turbopump on it, connect a roughing pump to that, bolt the thermoelectric vacuum gauge on, bolt a off-the-shelf HV passthrough to the chamber, plug in the HV psu, pump it down to 1 micron, backfill it with deuterium, flip the switch, bask in the neutron radiation. Easy.
The only thing that requires actual fabrication is the grids, which a competent welder can make in 20 minutes with a MIG and some bent stainless welding rod. Everything else is pure COTS.
If he didn't have $50k, then it could have been almost arbitrarily hard. A 40 year old two-stage mechanical pump+diffusion pump can do the high vacuum required, if you don't have the money for a modern setup-- only if you keep them flawlessly maintained, (including frequent oil changes, to replace the gunk that dissolves into it) and don't mind 24 hour pumpdown times. You can build your own chamber instead of using commercial flange hardware, if you've got a week of free time. You can kludge together a 75K HV PSU by running a couple microwave oven transformers in series, in a vat of transformer oil to keep them from arcing over.
Either this fusor was high-dollar legos, or it was an epic year-long engineering job. We don't know, because the article is a lot more interested in bureaucratic trivia rather than the fusor itself.