Building a chassis is a satisfying and educational experience. All you need is a steel chop saw, an angle grinder (two would be better: one with a cutting disk, another with a flap disk), and a MIG welder, and some magnets, clamps, and that's about it. The steel stock made up around 2% of the cost of my project. Shipping costs for various bits and pieces were considerably more.

If you trade the price of the MIG for a ready-made chassis, remember that you won't be able to make your own engine legs, wishbones, wing stays, etc.