that all depends greatly on the type of cichlid you want. rift lake, west african, and a select few americans.
i would go for a few shell dwellers personally. a little trio could go in a 5 gal if they were L. multifasciatus, but others need larger.
you could get 1 lonely shell dweller of any type (just 1) in probably as small as 2 gallons, (i would never do this to a fish, but it can be done)