Well, 3D Home Architect is only like $100 for their top of the line product (they have something that sells for $10), but I don't think that I'd do anything without a real architect. There's no way an untrained person could know all of the things that need to be known to design a house without a lot of training and experience. If you tried to design it by yourself and handed those plans to a contractor, you'd end up with way more cost in change orders than an architect would have cost you to begin with.