Yeah, definitely a lot cheaper. I know plenty of people use it, so it obviously works. I feel like I'd be inclined to go overboard sealing it though. But that's just me.
A buddy of mine years ago built a giant iguana enclosure using melamine. It was gorgeous. He's a carpenter as well, so he did it really well. He built it so that it could be broken down easily in case he ever needed to move it, which turned out to be handy. That may be something to consider depending how big you're going.