Saliya,
If you can - can you break this down a bit further..
2nd, 3rd, 4th synchros + gasket set from Nissan - under $400
R+R gearbox - $0 (self)
New thrust bearing - $50ish
New internal bearing set - $300ish (not $200, were unable to get from regular supplier)
Workshop labour to disassemble/check/reassemble box - $450
You said - R+R - $0 - do you mean it cost you nothing to pull it down and put it back in.. not quite sure what you mean..
$450 - was that pulling it all apart, putting in new synchros & re-pressing the bearings??
Seems like you did alright..