Getting the plutonium necessary to construct a nuke is *much* easier to get than uranium. Building the nuke, however, is insanely complicated.
Access to uranium = very hard; construction = very easy
Access to plutonium = fairly easy; construction = insanely hard
Hmm, I would say that access to plutonium is also insanely hard, as it implies that you already have a local nuclear reactor and reprocessing facilities.
The hard part about getting uranium is probably just the logistics of disguising your mining operation as a desalination plant, or some other type of metal mine. And then exporting the semi-manufactured product to a reputable-sounding customer.
It'd be much cheaper just to buy the plutonium from someone else, which is why it's much easier to obtain. A few million USD ought to cover it. Good luck building the bomb, though. The equipment needed to do so is ludicrous (because, in order for the chain reaction to occur, you essentially need a critical mass of plutonium to implode in on itself simultaneously with a margin of error as small as several billionths/trillionths of a second. Achieving the precision necessary for the bomb to work at all is insanely difficult.
Uranium enrichment is an unbelievably expensive, energy-intensive process that is simply above and beyond the capacities of most any organization or government. Even with $billions at your disposal, good luck getting some. However, once you have some, you can probably assemble a nuke in your garage in less than a day with materials you can purchase at your local hardware store.