if I do make a server running from my internet will I still have to pay for it monthly?
short answer no. Long answer maybe.
When i ran a home-side server for the Tf2maps.net guys on my connection surprisingly everyone had good speed. My advertised DL/UL is 10/1, i get about 9500/941. I would suggest you have a good connection and a good upload.
Next CHECK YOUR PROVIDER this is
VERY important. Some providers do not want you running a server period and if they do see you are running a server *its easy to tell with how much usage a server takes* most will not even warn you just SNIP and you have no net and now you gotta go through the bull of calling them, maybe pay more to turn it back on cause you broke their ToS.. etc etc...
Providing you have a very good DL/UP connection and also your provider is a cool... enjoy yourself =)
edit: wait i never knew you lived in Australia! Do you know Paul Hogan or have a pet kangaroo?