SkyWest provides two pants, two shirts (M&H), and a tie plus all the decorations. You are able to buy more, but that is what they provide. You then need to get a blazer ($150 M&H) or leather jacket ($300 Perrone) and the hat is optional ($60 Premier).
SkyWest does have a policy that all uniforms must be purchased from M&H or Crew outfitters but it is not enforced. In fact they gave me permission to use a blazer from a previous previous airline so I didn't pay anything for uniforms. The last airline I worked for had the exact same uniform but forced me to purchase over $500 in uniform pieces.