Sandvox ($57/97) is similar to
RapidWeaver ($79). The main advantage over
iWeb ($79) is that it (for now) still supports Tiger on PowerPCs in addition to Intel Macs. It publishes to MobileMe or to other hosts via FTP. iWeb requires Leopard. However, I must admit, iWeb designs are more polished than Sandvox.
Freeway ($79/249) uses a different approach for developing Web sites.
Dreamweaver ($399) is another tool. These have steeper learning curves.
Once a site is within one of the template-based programs, it is easy to switch from one design style to another. However, the applications are not interchangeable; you can't switch from iWeb to Sandvox or visa versa without entering all the data and images again. Considering the time it takes to build and maintain a site, within reason, initial cost for the application should not be your primary concern. Find something that works well and is easy to maintain. Demos are available.