uhm.... So when I gave $200 to CHANG's assistant at warthogs for a Pollyjuice potion.... that wasn't me just pre-buying one?... cuz i thought that that upfront cost was to buy one from their next batch.... but then when they offered it to me later I would have had to pay $900???!?!?!?! how do you even still HAVE that much money by that point in the game???? is there something i missed that gives you a disgusting amount of credits?
Sorry but all your facts are way off, you should replay the segments in question. Obtaining the needed money is possible, though you have to indeed play really well to accumulate that much. Check out this walkthrough and look through the teal colored stripes for all interactions that involve money!