Here's a selfmade Spreadsheet, kinda selfexplanatory.
Special on this one: You can put in your amount of gold you actually have and see what you get out of it and how many Stacks of leather you need to buy.

Also I locked the yellow cells so you can't change the formula by mistake.
Included is an english and a german version!
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Have fun w/ it.
Greetz, Ven~