Is Second Life free

Yes, for basic membership.

Second Life is FREE! You can create an avatar and explore SL as long as you want and never pay a dime. However, most residents find that they wish to go shopping and expand the look of their avatars, and this does cost money. How much money you spend in Second Life is entirely up to you though, just like in the real world.

You only need a premium account for some features such as renting land.