I often see in books phrases like "he paid XXX (in today's money XXX). How are these kind of things calculated if inflation in economic terms is based on a 'basket' of goods and services of today's economy?
Real wages, prices and so on are calculated on the basis of currency/gold standard. Various datasets have been cropping up in the past two decades that list every conceivable currency's real value over time, generally starting with the late early modern period. See for instance those released by the Global Price and Income History Group, or those systhematized by the social history institute in Amsterdam (iisg.nl, datasets section). I know this doesn't entirely answer your question, but I am sure a real economic historian will come along soon.