Sleek MakeUP Acid #6 is a cool blue with a frost finish that is permanent in palette and retails for $9.99. In comparison, Milani Bella Cobalt (25) is a cool blue with a frost finish that is permanent and retails for $4.49.
Milani Bella Cobalt (25) is 85% similar — it is less shimmery, darker, more muted.