I just replaced the transmission in my 91 so I have some recent experience to share.
If you're looking for a Nissan remanufactured, I believe the part numbers are listed below. Use the part numbers for price comparison purposes only.
3102N-51X65RE - Phase I -- 90-93 and
3102N-51X79RE - Phase II -- 94-96.
Based on your eastern US location, you are 4.5 hours from Charlottte NC. If you want to take your core for credit to Charlotte, I believe you can pickup a Nissan remanufactured transmission for approximately $1,559 + tax. The core credit for your old transmission is $400 -- so if you did not send in the old transmission, the price will increase by the core charge amount. You can avoid freight charges by taking the old transmission "South of the Border" to NC (or was that SC?) -- pardon the I-95 reference -
Also consider replacing the turbine sensor and rear main seal when the transmission has been removed.. It will never be easier to replace them.
If I were you and I valued the car as a keeper, I would borrow a pickup, and drive the old transmission to Charlotte to pickup a Nissan remanufactured - and enjoy the car for another 100,000 or more miles.
If you are a skilled metal fabricator and mechanic, and you have plenty of spare time to invest, then your out of pocket expense may be less going manual. But on one of these conversion jobs, your time can turn into money fast..