You can use any host and domain registration you like. There are a variety of inexpensive good hosting companies out there. Host Gator, QTH.com are 2 I know of off the top of my head. You can Google for more.
Depending on what you want to your PTO website to do will determine what platform you use. WordPress is great for simple things and there are plenty of plug-ins for calendars, pages for different areas, you can upload forms, etc.
There is a new company out there called DigitalPTO.com too. They provide a free basic PTO website (not your own domain though) as well as 2 upgraded options that will give you your own domain. The upgraded versions do have annual fees.
If there is someone in your PTO who is knowledgable about web design you can probably go with someone like HostGator, etc. and let them build it for you. I use WordPress for my personal blog and love the flexibility of it.
There are small companies that will also build websites and provide hosting services as well. Again, Google can find them for you. Keep in mind if your PTO is 501(c)3 you can have a .org instead of a .com
Here are some nice examples from our area -
www.soepto.org/
scepto.org/
schiffpta.org/
www.bmspto.org/
We don't have our own website yet but I'm working on it. I just need to decide what I want to present to the Board as far all of it goes. I'm still trying to find out the district's social media policy!