Going through the original Colonization's files, I noticed something: it's yield types had an "attrition" number assigned to them, which essentially meant that some yields (sugar, furs, coats, etc.) would slowly increase in price, and others (tools, muskets and trade goods) would slowly decrease in price, if left alone. In practice, this provided a certain recovery to original price levels, countering to a small degree the price changes caused by the continuous selling of goods such as sugar and rum by the colonies and their continuous buying of tools, muskets and trade goods. Think of it this way: each turn, colonial goods would accumulate a small amount of demand in European markets, while tools, muskets and trade goods would accumulate a small amount of supply in those same European markets.
This modcomp brings that functionality to Colonization II. To apply this to your mod, use the code under "//Androrc Price Recovery" in the C++ files, and add the necessary changes to the relevant XML files (in essence, add the "<iEuropeVolumeAttrition>" field to the yield schema, and add that field to each cargo yield (default value is 0). In the CIV4YieldInfos.xml included in this modcomp the iEuropeVolumeAttrition field is set in each yield to the same as it was for that yield in the original Colonization.
Europe Price Recovery 2016-10-05
Europe Price Recovery