rewsan: Not sure if I'm missing something here but before you enter the first dungeon you are given 20D in advance to buy equipment. However when I enter a shop I don't appear to have any more cash available than i did before I agreed to take on the dungeon. Am I missing something?
I presume you are referring to RoA1. Here are the things to note:
1) Your party members begin the game with money distributed non-uniformly (e.g. with the default party the dwarf starts with 120D, the next character with something else etc.), after you receive your first payment (20D 'upfront') the game will reorganise your money so it is fairly divided among each party member.
2) You will only receive your upfront payment AFTER you have first entered the dungeon, NOT after you have spoken to the guard (and been told about the 20D advance, and order to go ready your equipment). I have tested on my game, and the total sum after you have entered is equal to the old total +20D
3) There actually appears to be a bug in my game (not sure about others), whereby once you enter the dungeon and get the first 20D payment, you can leave the dungeon again and re-enter (gaining another 20D!) indefinitely - thereby earning an infinite number of Ducat! It would probably spoil your game though.
(also, just in case: 1D = 10S = 100B. When money is shared between party members, I think B values 0<x<1 are rounded down to 0...)
Hope that helped, but perhaps you already know the above. Enjoy the game!