ABOUT How much would a 5th generation or 4th generation tranny cost?Thanx for all ur help..

it all depends on mileage, but I would recommend you to get 5th gen tranny instead of 4th gen, since 4th gen tranny is expensive and most of them have somewhat high mileage. 5th gen tranny price is almost same as 4th gen but with much less mileage and stronger internal. If you search little bit you'll find out the advantage of 5th gen tranny over 4th gen tranny.
and the price is around $500-$1000.
search on www.car-parts.com

how much diff would it make 4th auto LSD vs 4th non LSD????

Brand new, the LSD is cheaper than the openend diff tranny. I don't know why but it is. A new manual tranny is about $1600 from everythingnissan.com. Not sure about auto.