I don't buy the argument. What if it does not become cheaper?
When many of the nuclear reactors were built, there was no pervasive global terrorism that is a threat to nuclear waste storage (edit: an nuclear reactors).
There are solutions, this is one of them.
You are right, things don't always improve, yet regarding nuclear power, they tend to.
There was no nuclear accident in 50 years in France, no public threat to nuclear waste storage so far. Pessimism isn't always the way to go.
It doesn't necessarily need to become cheaper in absolute terms, just cheaper than the alternatives of climate change damage. Those may continue to rise as we lollygag.
Do we actually have costs for the boreholes? Looking at the IDDP (geothermal deep borehole at 5km), I see costs of $22M. So we are talking about around $20B for the 800 boreholes forecasted for all the waste ever generated in the US. That sounds quite cheap to me.
When many of the nuclear reactors were built, there was no pervasive global terrorism that is a threat to nuclear waste storage (edit: an nuclear reactors).
Things don't always improve.