At the moment, these Ecopla are available at Bandai Hobby Center in Shizuoka only, and they are only on sales during the factory's annual open day. Some of them are actually being priced lower than their regular equivalences, but that doesn't affect their collection value at all ^^
Gundam RX-78-2 is actually one of the four releases for last year's Open Day. There are six this year, including that Guntank shown above.
Images from Hatena Diary: Gundam RX-78-2, Guntank.