@ maia0407
The idea of measuring the amount of bought ingredients by looking at the remaining gold is brilliant, and that alone should make a visit of this topic more than worth it for many people.
The rest is not quite as brilliant, especially the decision to add noise to this thread by publishing a private message, instead of simply replying in private and/or reporting it to a moderator.
For the 200 gold thing: after entering the amount of gold, the spreadsheet sits there waiting for the user to calculate the amount of lyrium in their head, or to arrive at some number by trial and error (taking care to keep the number a multiple of 4). I eased that pain by entering the formula "=4*FLOOR(C3/(4*C5+2*C6+2*C7+C8);1)"; for dealing with sets of whole stacks the last FLOOR() parameter can be changed to 99 or pulled from some input field.
Thereupon the spreadsheet proposes to buy 772 lyrium etc. but the exact numbers don't matter because the "Gold Tally" serves as a convenient guide when buying. Profit for the trip: 42.267 gold (21% ROI).
Alternatively, you could just buy lyrium in multiples of four stacks (9.50 gold per quadruple stack, i.e. roughly 10 gold) until the remaining gold drops below 102.07 which is 92.57 + 9.50. That would be 11 quadruple stacks in our example, for a profit of 238.49 gold (119% ROI). Or you could stop earlier, once the number of quadruple stacks times 21.68 gold exceeds the profit that you need.
92.57 is the cost of 99 full sets of the 'pub' ingredients, for minimum hassle and zero math effort. A reasonably convenient value for the less well-off is 46.83 gold (for a buy-stop when gold drops below 46.83 + 9.50 = 56.33). This still allows to buy the pub ingredients in stacks of 99, with flasks being bought only every other round, for at most four rounds before switching to full mode.
For example, if you only have 100 gold to your name then you could buy 384 lyrium as per the spreadsheet, for a profit of some 21 gold for the trip. Or you could buy 5 stacks of lyrium according to the half-set rule (stop below 56.33), for a profit of some 108 gold.
The buy-stop numbers work in either direction, Circle to pub and pub to Circle. When you're at the quartermaster's, the expected profit is a bit more than twice the difference between your gold and the magic buy-stop number.
This maximises the profit per roundtrip and minimises the number of required trips for making a given amount of gold. It completely avoids overbuy and the need to do non-trivial math in one's head or on a spreadsheet.