This year, I'm trying to garden year-round. It's a first attempt, and it may not turn out well, but I thought I'd share my experience so-far. I am, first and foremost, extremely cheap. So the idea of spending a lot of money so that I could garden in the winter just didn't appeal to me.
But it turns out it doesn't cost as much as you might suppose.
Here is my current setup:
As you can see, I've just got two half-inch, 10-foot PVC pipes stretched over each other. I tied them in the middle with some twine. They aren't really anchored to anything, just pushed down into the dirt next to the raised bed frame. It's then covered with 4mil plastic sheeting cut to 10x12 sheets, and then anchored down with bricks and logs and whatever I could find.
Anyway, hopefully this will allow enough protection to keep growing well into the winter. Anyway, it was worth the cost.
Here's the total breakdown of costs of each raised bed and the winter protection: