I haven't stripped a 25 box for a while but I think you can get rev and 5th off without pressing everything out of the centre plate.
From memory the genuine Nissan parts are not cheap it will probably cost between $400-$600 just in syncros, bearings, seals and oil etc. Just to do a quick repair.
Don't take this as gospel but it might be work asking the question if it can be done, good luck.