How do gambling costs increase as clvl increases?

[candlelight]

New info given below, and some confusion, based on a short experiment.

I recorded prices for three different items for a character gambling at level 73. Then I recorded prices for those exact same three items when that character advanced to level 74. Here is what I found:

gambling costs for normal gloves ...
lvl 73: 40650 gold
lvl 74: 41533 gold
increase in costs: 883 gold
% increase over lvl 73: 2.17220%

gambling costs for a light belt ...
lvl 73: 37816 gold
lvl 74: 38814 gold
increase in costs: 998 gold
% increase over lvl 73: 2.63909%

gambling costs for chain mail armor ...
lvl 73: 138657 gold
lvl 74: 143073 gold
increase in costs: 4416 gold
% increase over lvl 73: 3.18484%

Essentially, it seems that there isn't a uniform percentage increase in costs of gambling, per level, for each item. I can't help wondering if there are also differences in incremental gambling cost increases across levels, in addition to differences across items. Or, perhaps, there's a random element in the mix somewhere.

So that this can be replicated, I'll mention that my character was not using Gheed's fortune or an "edge" runeword bow. She had nothing exceptional on her that would have altered vendor or gambling prices in any way.