Exctractors are necessary Tools to extract Ores from Nodes. They are single-use devices, so quite many of them have to be crafted. Alternatively, Basic Extractors and Advanced Extractors can be found in Treasure Chests or can be more rarely obtained from Keepas of any kind and from Things. As for the Super Extractor; the Thing is the only source for the rare Recipe of this valuable Extractor that extracts more Ore from Nodes faster than the other two types of Extractors.
Excavators on the other hand are single-use Mining Tools for all kinds of blocks/materials EXCEPT for Nodes in an area of 7x7x7 blocks max. and listed in the section Explosives ingame. They remove all blocks up to a specific hardness (depending on the types of Excavators) and save half of them in Loot Bags. When the world or claim option "explosives disabled" is enabled, Excavators cannot be activated.