I had a Sliver Overlord EDH deck... And now I'm founding extremely hard to choose if the best commander would it be The First Sliver, Morophon or still is Sliver Overlord.... each of them has their pros and cons, so I'm still stuck xDD.
The lands will often be the expensive part, though there are ways to cut down on cost. The best option for the cheaper tribe I think is Elemental, good colour mix, support and low $$$. But Humans or Allys could be another option.