I found a great site that made it easy to set up a website for only $30/year: myschoolonline.com
If you don't have a computer background it gives you templates to work with. It only took me a few hours to put up a website that was pretty decent. Good Luck!
See if there is a parent / teacher that may be familiar with web design. Perhaps they would be willing to take on this task or assist you. Look into software (i.e. Front Page). If you are very comfortable with Word you will be off to a good start with Front Page.
You will also need a domain / host. You can probably find links to hosts from some existing PTO sites. Research the fees and exchange emails with the webmasters concerning what they think of the host.
Look at the PTO sites that are already out there. Note what you like or don't like. Note ideas that will work well for your organization.
Make a plan by drawing out the site on paper. Envision how it will work and function. Keep in mind dial up vs. high speed users when including graphics.