Hi all,
Thanks for the advice.

I happened to be in town and saw what appeared to be a fixed gear/singlespeed bike at a used-stuff store. I ended up getting it for $50.
I could tell it was a cheaper model from the garish stickers and tires (yellow!) but it should do the trick. I just want to try it out, and it wasn't a huge investment. And it fits wider tires which is good for the gravel roads here.
I didn't think it was too heavy, but when I got home and googled it (Takara something or other) I was surprised that it weighs almost 30 lbs. Good thing it's very flat where I live!

If it turns out to be as much fun as I hope it will be, I can always get something nicer down the road. But it should work for now!