That's in theory; in practice there is a bunch of resellers that are making crazy amount of money due to "merit pricing" that makes sense in a stable market, but not now. The places you mention are much worse off than by a simple price ceiling per electricity type.
I mean, whenever electricity is being exported at high cost, that high cost is an indication that this other place has it even worse; and blocking trade would make electricity cheaper at the exporting place, but cause a larger spike (and possibly even blackouts with the associated economic disruption) at the importing place and also remove the economic incentives to increase surplus production at places who can do it cheaper than others.