Earlier quoted context omitted.
The total cost for storing and securing shit for 100.000 years is also 'externalized.' Both costs are more or less impossible to establish upfront.
This cost would be much easier to calculate if every country reprocessed spent nuclear fuel like France does instead of storing it. Reprocessed MOX fuel costs almost ten times as much as enriched uranium, but the left over waste products decay to levels similar to natural uranium in 300 years instead of 10,000. Molten Salt reactors would probably make reprocessing cheaper.
Plus, as you suggest, no-one wants to buy the MOX fuel product because it's more expensive than enriched uranium.