I think a solid state dosimeter would be more useful, particularly if it had a current and a log mode, assuming it survived the EM pulse. They are smaller, similar in price (I've seen both starting about $350) and I know geiger need to be recalibrate regularly.

A scintillator might work, but I only know of them from theory- I have now idea how big they have to be to be effective. Apparently they glow when hit by ionizing radiation. If it is being all pretty and sparkly, you need to be going someplace else. :P