North Korea is one of the poorest in the world, and yet still managed to get to the extent of 200-kiloton thermonuclear two-stage weapons. (North Korea, though, benefits from having coastlines and not being a landlocked nation that might be successfully blockaded.)
Assuming that the willpower is no problem - a government is willing to let any amount of citizenry starve, and risk any sanctions - what is the poorest (or not necessarily poor, but just geopolitically weak) nation that could pull off something like this? Seychelles? Maldives? Equatorial Guinea?
Going to be hard to beat North Korea, though they had pretty extensive help, to the point that most of their weapons grade material probably came from China, as well as designs and parts (plus all the stuff they got from Russia as well). And they are dirt poor as a nation.
I don’t think there are any limits to how poor you are as a country wrt a nuclear program if you are getting outside help. If you aren’t, then it’s going to depend on what your alliances and trade connections are, as if anyone finds out you are going to be in a world of hurt economically and politically, so better have good alliances. If you do, then it gets back to the first point…how much help are your allies giving you?
Making a working nuclear device is just the first step. Then come all these extra costs, how much of these are required:
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Will they be designed to contain modern safety devices and explosives to limit yields in case of accidents (fire, dropping, crushing, ESD)?
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What kind of reliability do the nuclear weapons need? 30% or 95%?
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Delivery systems. How far do the delivery systems need to send this nuclear weapon? A few hundred miles: cheap. Many thousands of miles: expensive. Do they need to be able to penetrate anti ballistic missile systems or anti-aircraft systems?
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Do you provide robust security for all stages of the nuclear weapons life-cycle to protect against acts of domestic or international terrorism? Serious security that never ends is serious expensive.
One possible answer would be to use mid-1960’s Israel as a baseline. Google says GDP in 1965 was 3.7 billion USD, which I think is unconverted for inflation. (Search criteria: Israel GDP 1965) Adjusting for inflation puts it at 30.2 billion USD today. Going with the World Bank GDP figures, that puts the answer as Estonia. I think Estonia works in a few other ways as well. The population is generally well educated, and they’ve got an unfriendly neighbour to provide motivation.
Israel had some help, though - while it made the actual weapons itself, it was France that designed, built and paid for the nuclear reactor.
Even at the high end, $53 million isn’t a lot of money for a nation. Even a nation like Somalia has a GDP of 5 billion.
And I imagine that at least one or two of the weapons had to be tested somewhere…
North Korean nukes just have to make it over the DMZ!
As stated, they have two nations, China and Russia helping them behind the scenes.
BallistaNuke!
As for original question, i’d say you should look for the country that has motive, will, proper regime, resources, knowledge and time. In that order. And it does’t even have to be country. Can let we say Amazon do it? Or Ford? Or Musk. Maybe, but motive can be problematic.
Oh, it was…
Plus, Estonia has some uranium, though they ceased production in 1989:
If you want to presume that somebody could do it a bit cheaper because of lessons learned, etc, perhaps an outside shot would be Iceland - $23 billion GDP on that list. Given that they’ve gone crazy and are willing to bankrupt themselves to do so - they have no Earthly reason to WANT a nuclear program, either for power generation or weapons, but that wasn’t the premise. Also, given that they could trade for the needed resources, as mentioned. They are also a first world country with an educated population. They do have the advantages of a lot of available energy resources for manufacturing, and a lot of isolated locations for a small country, where they could conduct projects in secret.
That seems pretty unconvincing as evidence that ‘it was’…more like ‘could have been’ with a lot of ‘maybe’ and ‘possibly’ tossed in. If this was the best evidence that such a test or tests were done, all I can say is…it’s pretty weak.
The vast majority of the difficulty in obtaining nuclear weapons is getting sufficient quantities of the right nuclear materials - i.e. Plutonium 239 or Uranium 235. There’s basically one way each to get them- you create Pu-239 in nuclear reactors, and then chemically separate it from the rest of the fuel, or you isotopically separate natural U-235 from uranium ore, where it’s a very small component. Both of these are very capital intensive- one requires nuclear reactors and processing infrastructure, and the other requires Uranium ore, and some very involved separation/purification facilities.
So the presence of one of those two things- existing nuclear reactors or a pretty robust chemical industry would seem to be prerequisites for a nuclear weapon program.
The engineering of the warheads themselves only requires 1945-level manufacturing/engineering technology and know-how; I can’t imagine that’s much of a hurdle anymore.
Define “poor”. And GDP is really an appropriate measuring stick.
You need industry and a scientific and technical base.
North Korea has a pretty substantial industrial base.
I vaguely recall a 1960’s Dick Gregory critique of those poo-poohing China’s nuke program because China lacked delivery systems. With something like a billion citizens, he said, they could hand-carry their bombs anywhere!
Do old Soviet nuke components still appear on black markets? Even Vatican City could afford such.
That it was a nuclear test, or that it was Israel+South Africa?
Because it seems there’s plenty of actual evidence. Including radioactive sheep and acoustic data in addition to the well-known satellite data and corroborating South African testimony. And it’s pretty much an open secret here in South Africa, anyway.
The Duchy of Grand Fenwick was able to acquire a Q-bomb despite having no money for a nuclear weapons program. 
An atomic bomb explosion that doesn’t move any rocks or water?
Didn’t bother to read the rest of the page, I take it?
I read the whole fucking thing. Did you read my quote?