It really depends on whether you want a nice soldering iron or just something that will allow you to try it for a few hours. There is a huge price difference. Of course there is also a huge difference in quality. You could get a very nice iron like this for around $250. Or you could get something much less expensive, like this for around $40.

The first one I listed is very similar to one of the best irons I've ever used. The second one is still head and shoulders above the piece of crap I used for the first several years I was soldering. It was like this, at around $5, and as long as I kept the tip sharpened with a file it worked pretty well.