There will be some Dzialki in Mokotow that will be freed up soon (they have to change some laws.) They'll probably go for pretty cheap (prime property that will skyrocket soon after.) Anyway, this is what my student tells me.
If you are looking for land around Warszawa, firstly take into consideration the new ring road that will be built. I would suggest the area around Podkowa Lesna, This area will be a competitor to Konstancin over the next 10 years. The infrastructure is good and it is close to the roads leading to Wroclaw, krakow and Poznan. But you do know that as a private person you have to get permission to buy- unless you buy through a Polish passport holder or registered company in Poland
Polish People also have a real obsession about forests and having a plot with trees on it.
I've got building land to let or for sale in a beauty area near Otwock 40 km from the center of Warsaw in Poland. It's quite cheap so far. If you need some information: @wp.pl