They usually offer you a special price just when your trial is about to expire - from memory it was $US16.95 for 90 days. Or you can pay $US10 for 30 days - I recently did this and it was only $10.50 Australian.

You get more analysis if you pay - you can see patterns and graphs, overlay your charts, have access to the FF guides and message boards, I find it quite useful. But if you don't care about analysing etc then the free way is fine, your info will still be there.