Most websites suggested are free. The follow links are to the premium content and pricing for the various sites. The sites can be used instructionally in free mode. You may decide that some sites premium content is of value in your classroom.

TodaysMeet Subscription: https://todaysmeet.com/accounts/upgrade
Starfall: http://more.starfall.com/info/educators.php
Newsela: https://newsela.com/about/
Little Explorers/Enchanted Learning: http://www.enchantedlearning.com/support/index1.shtml
Diigo: https://www.diigo.com/premium
Educreations; https://www.educreations.com/pricing/
Classtools: http://www.activehistory.co.uk/classtools_premium/index.htm