No...you don't have to pay for it. Everybody asks me this!
(if you have a copy that is expiring, it simply means you need to install
the 'still free' update) 

Just because they WANT you to buy it (can you blame them?), the good people
at Grissoft still provides their free, excellent Anti Virus program.
Simply download the AVG Free program, and install.
When prompted, choose "repair", and your old version will be updated to the new
(free) version.