The Turkish e-Visa is an official document permitting entry into and travel within Turkey. 

Applicants obtain their visas electronically after entering required information online and making payments by a credit or debit card (Mastercard, Visa or Paypal).

You need to have a travel document (passport) valid for at least 6 (six) months from the date you intend to enter Turkey. 

Depending on your nationality, there may be additional requirements. 

The fee actually depends on your nationality. 

You can apply here: https://turkishvisa.com/