Well, I have just set up webcams without using a dedicated IP address and they seem to be working. Tricky bit of software to run them. BTL told me that there were three levels of service re IP addresses - totally floating, floating within a restricted range, and fixed. It wouldn't surprise me to find that wasn't true, mind. They are pretty hopeless on giving information.
I had a static IP address in the UK without there being any extra charge, but we're talking about Belize which has bought way too few IP addresses.