I know there are some wonders that modify the amount, but what I'm really looking for is information on what factors determine how much each tile costs, since they seem to vary per-tile and over time (and/or if you purchase tiles).
In my experience, the factors which effect purchase cost are:
- Current turn/era (the later the costlier)
- Number of tiles the city already has (the larger the costlier)
- Distance from the city (the further away the costlier)
- Whether the tile is one which is considered for expansion - i.e. has a purple border (if it is, it's about half the price)
For a more complete reference, below is the section from the game configuration file which deals with "acquiring new plots", as it is called there. Any entry with "culture" applies to culture "cost" only, but I'm not quite sure what the entries with "influence" mean; perhaps this applies to both gold and culture cost.
(the section was originally in XML format, but I've changed it to something friendlier)
Cost of acquiring new Plots PLOT_BASE_COST = 50 PLOT_ADDITIONAL_COST_PER_PLOT = 5 PLOT_COST_APPEARANCE_DIVISOR = 5 CULTURE_COST_FIRST_PLOT = 15 CULTURE_COST_LATER_PLOT_MULTIPLIER = 10 CULTURE_COST_VISIBLE_DIVISOR = 5 CULTURE_PLOT_COST_MOD_MINIMUM = -85 MINOR_CIV_PLOT_CULTURE_COST_MULTIPLIER = 150 MAXIMUM_BUY_PLOT_DISTANCE = 3 MAXIMUM_ACQUIRE_PLOT_DISTANCE = 5 PLOT_INFLUENCE_DISTANCE_MULTIPLIER = 100 PLOT_INFLUENCE_RING_COST = 100 PLOT_INFLUENCE_WATER_COST = 25 PLOT_INFLUENCE_IMPROVEMENT_COST = -5 PLOT_INFLUENCE_ROUTE_COST = 0 PLOT_INFLUENCE_RESOURCE_COST = -105 PLOT_INFLUENCE_NW_COST = -105 PLOT_BUY_RESOURCE_COST = -100 PLOT_BUY_YIELD_COST = 10 PLOT_INFLUENCE_YIELD_POINT_COST = -1 PLOT_INFLUENCE_NO_ADJACENT_OWNED_COST = 1000