Well there is quite a difference between a chain harrow and a chainlink drag. A chain or blanket harrow has teeth and is made up of a bunch of twisted interconnected links. The teeth can be down and forward(agressive cut), down and to the rear(less agressive), and teeth up which provides smoothing similar to a chain link fence drag.
If you just want to smooth something, that is already relatively loose(like an arena or driveway) a chainlink drag is easy to build and relatively inexpensive.
If you want to rip/breakup the soil, such as to put down seed for the food plot, you are going to need something with some teeth.
The difference between the chainlink drag and the chain harrow is like the difference between 40 grit sandpaper and 250 grit sandpaper.
I don't think you are going to easilly be able to fabricate a chain harrow as there is a lot of bits to bend up and interconnect. That is probably why they cost so much. You might also find it difficult to tow with a quad or lawn tractor. I have a 5' square one, and I can barely tow it with the teeth up with my 27HP sears garden tractor, teeth down, I might as well be trying to tow a live oak tree... They have a lot of drag towed teeth down.
You might try something like a thatching rake with weight on it to break up the soil and clear off the debris so the seed will find the soil. Then follow along with a chainlink drag to help cover the seed.
I have used heavy wall pipe for the chainlink drags I have built in the past. I fold the chainlink around the pipe and lace it to itself. I then weld/attach the drag chain to the ends of the front pipe.
