I think Omnipitent checked - they want $800 - might as well buy new. I would be looking for a "close" aftermarket replacement if a repair is not possible.
I was wondering what type plastic it is too, but I've repaired some plastic stuff in the past with limited success. anything that gets cycled between hot and cold with plastic and metal doesn't seem like a good choice of materials to use. I can't imagine any repair to that plastic tank that I would put trust in. Honstly, I hate it when I see plastic parts used on engines. Some parts are fine depending on thier purpose and type of polymer it is. When I encounter a failure of a part on my stuff, I look to replacing it with something better than the original, which usually involves exploring salvage yards or fabricating a new part or modifying the original so it won't ever fail again. The downside of what I do is it takes more time to complete the fix vs. replacing the part with another original design part. I guess I'm stubborn and cheap, but I don't end up getting angry over another failure on the same component. Tractor parts are ridiculously priced. I suppose if you need it fixed sooner than later you could try scouring the interweb for used replacement parts that will just bolt right in and get you moving again for a little less moolah than $1000 bucks. I wish you luck Citydude. Please let us know how you make out.
That's the best solution if you can get it. It's worth the effort.
To all you making fun of a JB Weld radiator repair, all 3 such emergency radiator repairs I did over the years never failed. Presently driving a Toyota with a JB repaired radiator done 15 years ago & never failed. (yet) In a pinch I would do a JB fix and (maybe) eventually replace the rad if it made me nervous. I'd clean it up really well and lay in some reinforcing material to widen the holding area. Just do it.