Nemesis skins feature a custom painted image of a metallic monster. Currently, there is only one member of this family which is MP7 | Nemesis. This skin was added to the game in May 2015 during the Operation Bloodhound update and can be obtained by opening the Falchion Case. MP7 Nemesis is a member of The Falchion Collection and is only available in three exteriors, Factory New, Minimal Wear, and Field-Tested as well as their StatTrak versions.
When it comes to the price, it can vary from around $5 up to $40 depending on the exterior as well as whether the skin has StatTrak attached.
Check out other CS:GO skins families: