Why do you think that the cost has to be equivalent? The difference of cost would be a perfect measure of the strength of that desire; if people would be willing to pay a significant premium to get X, then that's a credible sign that they desire X and it matters to them; and if they're not willing to pay a nontrivial premium to get X then clearly it's not valuable to them.

The qualifier about perfect information and comprehension is legit, but given that, if you'd choose decentralization only if the cost and other circumstances are equivalent then that's a sign that decentralization is worth zero.