Around here I can buy old section spike harrows for $20/section. I bought two so I have a ready supply of spikes. I prefer to drag mine, as there is a lot of sidehill in my garden, and corn patch.
Just remember - not a rebar is created equal! The stuff you buy at Home Depot or the lumber yard is grade 2. Go to a brige sit and ask them for scraps. This will be grade 4 and be hard enough for your teeth. The RR spikes work great also, if you can find them. Scrounging for an old harrow is what would be best. Aslo, consider a "tine" harrow which uses the spring teeth from a baler or rake. Easy to build and easy to get parts for.