Land expansions
  Level Costs in island dollars Costs in gold
Expansion (Land) 5/25 10,000 50
  6/25 59,000 350
  7/25 95,000 900
  8/25 175,000 1,050
  9/25 280,000 1,250
  10/25 430,000 1,500
  11/25 600,000 1,800
  12/25 820,000 2,150
  13/25 1,100,000 2,500
  14/25 1,500,000 2,850
  15/25 1,900,000 3,200
  16/25 2,500,000 3,550
  17/25 3,100,000 3,900
  18/25 3,900,000 4,250
  19/25 4,800,000 4,600
  20/25 5,900,000 4,950
  21/25 7,100,000 5,300
  22/25 8,500,000 5,650
  23/25 10,000,000 6,000
  24/25 12,000,000 6,350
  25/25 14,000,000 6,700
   
  courtesy of Larino's Corner: spreadsheet