So many times I'm reading a Victorian plot that revolves around some gentry fop handing a scullery boy a sum of 100 half-whatevers. And I'm left wondering: is that a staggeringly large amount of money or an insultingly small one?
Historical Currency Conversions is a tool for finding the current value of historical currency. Type in an amount you see in a book and it spits out: "100 guineas in 1850 had the same buying power as 14647.25 current dollars." Sure there are socioeconomic challenges to comparing 1850 London with current times, but you get in the ballpark enough to move on with your book.