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It really depends. Region to region, server provider to provider. You can actually host all the hardware yourself and have huge startup cost but basically no ongoing cost. The real cost so to speak, I would say, is time. As you need to maintain the node. As of HF23, no matter the region, I'd say about 100 USD to startup and more or less the same for the ongoing cost (excluding time) however, HF24 really changes things and it becomes a lot more efficient to run nodes. But we'll see :) I can't really give a good answer for HF24 yet as it is yet to be tested.