an ADVISE regarding the levitation of the price of the goods purchased:
phase 1:
single purchase: The price could be blocked at the value in which it is found by the merchant until the end of the day in which it is bought (100).
purchase in blocks: Moreover, if one takes the same object in blocks, therefore starting from a certain number fixed by the merchant, the price, from constant and fixed, starts to decrease with a downward trend up to a minimum threshold always fixed by the merchant (maybe 80% of the base price with a matematic function.)
100 (for 1 weapon) -> 95 (for 2-3) -> 90 (for 4-6) -> ....--> 100 * (%) (for N-1, N)
let's keep aside the same price increase already present in bannerlord, because nothing has to go to waste, so we'll use it for phase 2.
phase 2:
at the end of the day the purchased good is put on sale starting from the maximum value that would have been reached with the bannerlord variable price system in real time (100 -> 106 -> 113 we suppose).
In addition to the maximum price (113 we suppose) there is an increase in this base price equal to the% discount that they did last time.
so let's suppose that last time they gave us a 20% discount.
the price would be:
113 * (1 + 20/100) = 135.6, which is approximate 136
maybe 20% off is a lot, because the risk of a merchant would be to sell a little immediately but a lot and not sell in the future because the prices go up too much.
In this regard, if the economic system over time does not dispose the merchant of this good, a formula can be adopted that shows the price of the good at 113, without the 20% increase,after a certain time.
for example:
formula for decreasing the price increase:
F (t) = 1 / e ^ (t / (G-t))
G: maximum days for which the surcharge is greater than 0.
t: time (in days)
when G-t -> 0, 1 / (G-t) -> infinity and F (t) -> 0
With 0 <= t <= G
in general:
if P is the price of the weapon and 136 with a 20% increase, you have:
P * (1+ (X / 100) * F (t))
with P = 113, X = 20 and t = 0 we have the maximum price at the end of the day of the first transaction, ie 136.
if we set G at 10 days, the price is reduced over time up to 113 on the tenth day.
This without having taken into account the variation in the price of the weapon due to the basic system (ie the variation of P from 100 to 113 and vice versa).
if you want a softer descent than the percentage increase you can replace F (t) with
F (d) = 1 / log (e + (d / G-d))
with 0<=d<=G
in short, the mathematical functions to do this are not lacking, it is enough to choose the one that is considered most suitable for the purpose.
if the variation P is taken into account through the basic price increase system, then the prices will vary even more, but only at the beginning of the day after the transaction.