I probably don't have a fixed IP address
That part is easy to address with dyndns or various other services.
I'd have to keep on top of security far more closely than with a PC
That depends on what you need. If all you need is to host a static website, the security concerns are actually pretty minimal. If you want php and a lot of goodies plus remote login and what-have-you then your concerns grow quickly.
I'd have to have at least two computers running 24/7/365 in case one went down, and I usually only have one or two running when I'm awake
Perhaps I underestimated the traffic volume for your web site, then. I know if my site is down occasionally (my personal server at home pulls five nines without much effort but there are sporadic things beyond my control like power / internet losses) it isn't a big deal.
The electricity alone would cost more than hosting.
I wouldn't be so sure of that. Again, if it is just a static page you could set up a really basic box (think mini-ITX) with as few moving parts as possible and your power consumption will be less than if you go to work and forget to turn off your coffee maker on the way out the door. I can tell you that the power consumption of my web server at home (an old P4 desktop I got for free some time ago) makes no notable difference on our monthly power bill.
You may have seen some of my JEs over the years where I have mocked the various attempts to compromise my home system via ssh. If I bothered to either change my ssh port or disable ssh entirely I would have basically zero attempts - I leave it where it is primarily out of laziness and my occasional needs to check in to my system remotely for various work-related functions.