are you sure? the base 100,000 would net you 2,000 testimonies, each worth .50e, so 1,000 echoes. hinterland prosperity, only after you've maxed out efficiency (which is a long undertaking itself and based on luck, AND doing this resets it) awards 550 per average prosperity-increasing action on a card. so it takes roughly 182 straight actions of raising prosperity to get to this amount.

182 actions to get 1,000 echoes, unless I'm stumbling somewhere, is 5.5ish EPA before counting any other action that goes into it, i.e. gathering favors, failures due to this being a very high check, and the efficiency loss if you're planning to recoup that afterwards

unless I'm missing something, which I could be, that doesn't seem worth it at all