Do you have a core? I'm pretty sure you can get a rebuilt for under $2k.
Without a core, I would give PEDCO a call in California. They might have what you need.
No matter what, you'll need to send whatever you get to Allison for programming -- somewhere between $500 and $1000 IIRC. You'll need the serial number from your transmission so they can put the factory program back in. You can have changes made to the program for an extra charge.