Mitsubishi Forum - Mitsubishi Enthusiast Forums - 1985 Montero

Does anyone have an idea of what I can expect to pay to have a transmission rebuilt in my 1985 Mitsubishi Montero? It's a 4X4, 4-cyl manual transmission with 140K+ miles.
Problem began with the first-rebuild 4 years ago. Shifting was chunky after that job and remained that way. 6 months ago 5th gear began slipping into neutral on the freeway (I must hold it in 5th or cruise in 4th). Lost ability to downshift from 3rd to 2nd. Clanking metallic sound when I shift gears. I began losing Reverse two weeks ago.
The car is ambulatory but who knows when the transmission will cough its last cough. I am trying to determine the total cost and time it will take to rebuild along with the terms of your warranty.
I got one quote of $2000 with an 18-month warranty. Is that high?
Thanks.