Other folks have commented on general pricing, and you can't go wrong with a wheel rebuild. My last bike was having cascading spoke failures, and a complete rebuild did the trick.

But, replacing a single spoke isn't so bad if you have the tools. You can true it reasonably well by eye. If you have good ears, I like to strum the spokes to hear the sound they make, and match pitch with other spokes on the same side. I replaced one spoke on the side of the road like this and the wheel has stayed true.