Initial Investment / Level Requirements:
I do not know how much weight you put into this requirement either, but I do have an opinion on how much weight it should have. Typically, in any real life adventure, an initial investment is one that is meant to be paid off in time. IE: If I spend this 1000 Marble and 1000 Hardwood to make a stable, I should not make my investment back within my first few sales, it should take some time to recoup. If I can sell my first 800 horses in 24 hours, and recoup my investment, via selling horses for gold, and then trading coins for HW/Marble at your ratios, I do not see it as being a huge determining factor to the increase in the price of goods.