I just remembered this response and have stopped procrastinating on answering it.

Just so I'm clear, and maybe this is a dumb question, but you can request data from mesh nodes that you don't have physical access or line of sight with, right? As long as you can connect to the meshnet, you can connect to every server on the entire mesh network, right? Like you can hop 2 or 3 nodes away to fetch data, right?

Yes.

Also how good is the coverage of the meshnet? If the internet goes out for the whole world, can I communicate across the US with it? Does it span across the whole world?

Pretty low, unfortunately, due to low traction. Having SaidIt on it might be able to provide more uses for it though, thereby attracting more users. I don't believe it spans across the whole world yet, or even the US, but Germany has pretty good coverage among other places. I may want to seastead in the future, so this might work well for relatively cheap intercontinental meshnet communication without relying on the internet.

What's the cost for the antenna and signal booster and electronics needed to create a node? Like $1000? Is it doable for like $200? That'd be a price we could actually consider getting started on that right away

I believe there are some materials around that price, although it also depends on how far the nearest node is. You may be able to find more information in /r/darknetplanhw.

If that works out, I want free/cheap meshnet hosting for saidit for thinking of the idea please ;)

I would be more than happy to help with hosting on both meshnet and clearnet! Server hosting is one of my most favourite things to do, especially when it helps others! I have a dedicated computer at home with 2 Xeon X5560s, 24GB of RAM, terabytes of hard disk space and a massive amount of room for expansion. I also have a VPS with 2GB of RAM I am struggling to pay $7/month for, since the service I run on it isn't quite profitable enough. The biggest bottlenecks of my home server is my 5Mb/s upload speed, fairly bad latency, internet and electricity that rarely goes out, and a computer that even more rarely goes out, but has before due to me accidentally using too much RAM, which is why I upgraded to 24GB in the first place. I usually have over 8GB free, and I have over a terabyte free on all my combined drives and can trivially free up around 500GB on one of them resulting in almost 1.5 free terabytes on one drive.