skorgu

  iss_mass = 419600
  sep_isp = 4190
  delta_v = 5748
  htv_payload = 3310
  falcon_launch_cost = 62000000
  total_mass = iss_mass * math.exp(delta_v / (9.8 * sep_isp))
  fuel_load = total_mass - iss_mass
  dragon_launches = math.floor(fuel_load / htv_payload)
  total_cost = dragon_launches * falcon_launch_cost

  Total vehicle mass: 482,646.89 kg
  Fuel to add: 63,046.89 kg
  Dragon 2 launches: 19
  Total cost: $1,178,000,000.00

  [0] https://en.wikipedia.org/wiki/NEXT_(ion_thruster)
  [1] https://en.wikipedia.org/wiki/Electrical_system_of_the_International_Space_Station