Ok look I'm only a self-proclaimed mechanic but I hold no certifications or licensing. Disclaimer....no...honesty. But I can tell you that if you're not afraid of getting dirty and can at the very least practice "Safety first!!!" I'm beyond confident that you can save a few bucks on the installation of your transmission. Salvage yards can supply decent trannies for under $500 and with a little "gangster" you can strong-arm one in on your back. I've done it w/both rear-wheeled and front-wheel drive vehicles the latter being most difficult primarily due to extra weight of the included differential. Help from a Haynes or Chilton manual on your model year and a good set of hand tools. Expect to use a torque wrench w/an array of metric sockets, a good floor jack as well as no less than 4 jack-stands(2 for safety in case the other 2 malfunction), screw drivers, 2 wheel chucks and maybe a breaker-bar. Rear-wheel drive trannies come out pretty easy as longs as you disconnect everything first. 1. Rear yoke of driveshaft(pull front splined end of driveshaft out of the rear of the tranny and set aside) 2. Remove dust shield from torque converter section(front-most section) and with the neutral range selected unscrew each T/C-to-flex-plate bolt rotating the flex-plate clockwise to the next bolts in succession.(you may disco your battery and remove your spark plugs to prevent compression in your cylinders making it easier to spin the engine/flex-plate. 3, Disc your range selector(gear-shifter) recording the steps taken in doing so. record the whole process for ease of installation. 4. Support your tranny under its oil-pan w/floor-jack then unbolt your transmission cross-member from the tranny and then the frame-rails. 5. Unbolt the transmission bell-housing-to-engine bolts. 6. If all bolts are out you should take care to hold onto the tranny as you pull it rearward and free of the engine.(floor-jack should roll w/tranny atop fairly easily) installation is the reverse of this. Do jack your Pathfinder up as high as possible to allow freedom to maneuver under it. Hope you give it a shot. Be safe!!!!

Before you go and pull the transmission rearward you want to slowly move it rearward in increments and keep the torque converter pressed against the transmission. If you don't it will slide off and fall onto the floor making a big mess! I put a piece of 2x4 against it then ran a long zip-tie across the front-keeping the wood against the TC. That way you won't have to worry about it when you are lowering it and moving it around.
ALSO, before separating the tranny/engine you need to disconnect the plug for the flywheel sensor! If you don't, you will break the wires. It's located on top of the tranny and is a pain to get to. Reconnecting it when reinstalling the tranny is a bigger pain in the shorts!

That's why two heads are always better than one my friend-- and I haven't done anything with a pathfinder tranny yet, as that was just my general instruction based on a RWD. There could be more that I've left out in regards to this tranny. Definitely watch that torque-converter it surely leave a mark if it happened to fall on you. Safety first!!!