I have no way to estimate a complete engine replacement, so here's our estimator link, it may be of some help.
As far a saving money, be careful. Remember: "Cheaper, or better job: Pick one."
I understand saving money but the primary interest is fixing the car properly the first time, you may pay less and get less quality if you try to be too "thrifty." The best thing to do is find an independent Nissan specialist. That's how to get your money's worth..
If you want to find a specialist, here's our directory link for you: