PLA spools can be as cheap as $15 per kilo. There is pretty minimal waste when printing (depending on how much support is needed for the print), so the material cost is pretty low. Printing that may lowers would take a ton of time tough. Since he had no intention of using them, he could have used a reduced number of walls with minimal infill which would have helped to reduce print time, but printing all those on a single small printer would still take quite a few days.