No, not lifetime. Permanent. For as long as LiveJournal exists... which may just be longer than you do. In addition, you'll also get a ton of space on the LiveJournal image server (which is what we're going to do with our current database server.)
Why the need for money? Because LJ is growing really, really fast... and needs to have a really, really fast database server to keep up with it. Looks like we've settled on this one. It's very scalable and should rock our world for a long, long time.
Assuming you don't have $100 sitting around, however, you can always either purchase or extend your existing membership by whatever you can afford. Every little bit helps!