They are Epic 40,000 Ork Wirdboy towers, as mentioned above, and they used to come two to a blister.
Not sure how rare they are, as they came towards the end of the Ork releases IIRC, and it was more efficient to just buy the Weirdboy and stick him in a Battlewagon than buy the Battlewagon the Weirdboy upgrade.
Besides which, they were trivially easy to convert from plastic Battlewagons - so by the time of their release, most people had the ones they needed all converted up anyway (or just used the old Epic Space Marine ones, which came three to a blister).
As a result, you tend to find them in new condition quite often whenever they come up.
Link
here for you.
