I would think you could beat that $700 by a good bit. From what I've seen, at least in my neck of the woods, forks are by no means an endangered species. I paid under $100 for mine.
I built my carriage from nothing more than an attachment plate, two pieces of sturdy angle iron, and a short piece of flat bar. It took me 3 or 4 hours, and I'm no professional welder. A real welder should be able to do it in half that time.
With the cost of the attachment plate and steel stock, mine still cost less than $300 in materials. I could have saved nearly another $100 by building my own attachment plate.
I'm not sure where I put the photo files, but if you search for the "Meet Kermit" thread, there's a photo or two that might help.
The difference between that $700 estimate and the materials cost could buy you a decent basic arc welding outfit, if you're so inclined. If you figure it at the PT $1600 price, you could probably take a welding class, and buy a torch setup and a chop saw, too...
Whatever you decide on, enjoy it!
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