The Shadow perhaps ? Seriously though, the devs have not yet released that information. Honestly they probably have some basic nebulous number in mind, but will have to play-balance it a bit before nailing it down to anything specific.
So at the moment nobody knows because the value of gold or whatever currency SotA uses is unknown. The best way to think about it at the moment is in hours of play rather than currency. What we do know is that owning land is a challeng, rent on 1 plot is affordable, 2 plots only with lots of hard work and many hours of play, 3 plots would probably be impossible without help (info taken from IRC a month or so ago). So maybe the average player might put in say 60 hours of play a month, the upkeep on a plot of land could be the equivalent of 40 hours gold farming. 80 hours for 2 plots would equate to a heavy gamer. Have to also consider that the cost is ongoing.