A: Yes, it can be.

The basic account, which is free, is everything you need to do almost everything you'd want to do in world. Oh, sure, to become a real-estate mogal in SL on a basic account will take a bit more savvy, but the usual activities (touring, role playing, buying and selling stuff, aven building) can be done on a free account.

If you get into the game - and it can be addictively fun - you'll probably want to upgrade to a premium account at some point. The premium account allows you to buy land directly from Linden Labs (or Governor Linden, as the land manager is known in world). This land is more permanent and less restictive (no covenants) than land you buy or rent from other players.

Now, to be complete in this answer, you should know that players can spend a lot of money on the game if they want. Some parcels of land can get very expensive - hundreds or even thousands of dollars. Even without buying land, it can be easy to spend US$40 - US$100 per month in world buying cool clothes, avatars, vehicles, and other goodies.

But please remember: you can have all kinds of fun in world without spending a dime. In fact, some players love the angle of collecting freebies, trading goods with other players, and just finding folks who give them free stuff. If you are polite and genuine, and you have a real project you want to complete and don't ask for the world, many players in world will help you get what you want just out of the goodness of their heart.

Of course, other players will shoot you dead as look at you, so choose your folks (and places) for friendly requests for stuff wisely.