Aluminum is another option you can probably spend a bit less or get a bit of a larger pot for the same money. Here's an example: http://www.amazon.com/Imperial-MW120.../dp/B0072NBC00
I have a 15G bayou classic that looks like that one that I'm still using as a boil kettle. When I first got into brewing I bought an 8 gallon stainless steel pot that is just chilling out in my garage unused now.
I'd almost recommend shooting straight for a larger kettle. 10-15 gallons. It's more pricy. No reason you couldn't start with a smaller pot of course. Depends on your personality and what you're interested in. I only did a few batches on my smaller pot before I decided I really wanted something larger so I kind of feel like it was a waste of money (I spent more than $25 though
). I had some boil over issues in the 8 gallon while doing full volume boils.