Most plans will cover a dermatologist as a specialist visit. Refer to your policy to see what your specialists visits will cost. If you don't have your policy, call your provider. If you have your insurance card, check for a customer service number and give them a call. Specialist rates are often twice what a primary care physician co-pay will be.
Depending on the type of insurance that you have you may need a referral to see the dermatologist and have the visit covered by your health insurance.
You would get the referral from your primary care physician.