One of the wheels on my garage door came out of its bracket today and won't close. Thankfully, it's in the up position. I don't know if had come out already, but it worked before and now does not. I took a picture of it:

Is this something I can fix myself? I'm smart, but not particularly handy. It did not seem to move easily, though I didn't inspect it too close as it was pretty cold day. If I can't fix it myself, how much is a repair going to cost me, ballpark of course? Thanks for any help.