One of the things that people ask me about Second Life is "How much does it cost?" You can get an unpaid account for free, but here's a paid account example from one of my avatars. I have an annual account that costs me US$72/year. Each week Second Life distributes a 300 Linden dollar (L$300) stipend to each paid user's account*. That comes out to L$15,600/year. I just sold L$19,495 this morning and, after processing fees, received US$72.08. If we use this as a conversion factor the L$15,600 it comes to a little over US$57.67. So the true cost of the account is US$72 - US$57.67 which comes to US$14.33/year or a little less than US$1.20/month.
*This isn't entirely true. Users who created or upgraded to a premium account prior to November 2006 actually get a larger monthly stipend.