I love WordPress for websites. I've built several websites, and truthfully, I really don't know what I'm doing. And yet somehow it still works out okay in the end.
Someone below mentioned the district's social media policy. Are you talking about the comments section of a blog? You can easily turn off comments on any pages, and the default setting is for the administrator of the site (you) to approve any comments before they go live.
I use GoDaddy.com for hosting and it costs me something like $46 per year for my hosting. I have room for several small sites at that price (different domain names). I build simple sites for my friends all the time and I can host all of them under that plan. They have 24-hour technical service based in Phoenix, and they never make me feel dumb for not being technical. I knew nothing about hosting my own site when I started, and they held my hand and walked me through it, very gently.
Have you asked around in your school to see if there is someone like me who would be willing to build a simple site as a way to volunteer for the school? I'm a big fan of hiring a pro in most situations, but if you want just a simple site, asking an amateur can be a good way to get started.
One word of warning if you choose this path: I always tell my friends that if I build a site for them, they're getting what they pay for, and I'm never offended if they decide to scrap my site after a while and go with a pro. I'd make sure the person who builds your site feels the same way or a bruised ego is a guarantee.
As far as a Facebook site is concerned, I'm not for it. Facebook has control of this content, not you. They make the rules and they change them any time they want. You'll have advertising all the time (their choice of ads) and when they make their changes, is someone from your school going to be available to make sure the site is still running smoothly?
I love the idea that a website can help the parents stay updated with what your parent group is doing for the school. What a great way to remind them of the value of what you're doing, and then maybe they'll want to get involved as well!