I fully understand the budget deal. My brother in law has a 2000 6-cyl Mustang with a 4R70W in it... I believe the 6 cyls are Windsor pattern also. He's parting the car. It's not going anywhere anytime soon, so if you get the itch, I can ask him what he wants for the trans.
Bill Smith Auto Parts is another place to get good cores / used stuff cheap.