A small, shitty one is going to set you back over a hundred grand. Probably the same again in operating costs: like a competent technician, and liquid helium and nitrogen to fill it and keep the magnet superconducting.
A big one, for any serious research is going to cost a million. Dollars, Euros, Pounds, doesn't matter, I'm just saying the ballpark.
For the biggest ones, for real hardcore work, times that by ten, and add the cost of a new building to store it because they're fucking huge.
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