[martijnarts]

Somewhere up to $5 million, according to this r/AskEngineering thread: https://www.reddit.com/r/AskEngineers/comments/1dfzwxd/estim...

[daneel_w]

Which as with everything else in construction these days ultimately ends up taking twice as long and costing thrice the initial estimate. Also, this is the cost for a bore hole. The cost for something with enough diameter to house a reactor will be some orders of magnitude higher.

[martijnarts]

The article mentions 76 cm width for the reactor they're designing, and oil wells can be up to a meter wide[0], so that price estimate would probably be similar then.

[0]: https://en.wikipedia.org/wiki/Oil_well#Drilling

[themaninthedark]

Not as high as I thought it might be, as long as it is less costly than the containment vessel that they are looking to replace it would be a net.