New Engine

[RidgeRunner]

I don't want to slam the mechanic or anyone else, but a 95 and a 05 Merc are going to weight in about the same. Same displacement (2.5L) just a different fuel delivery. Fuel mileage is not going to be that much different either. If the 05 is EFI you might pick up a little fuel mileage but not much. If the 2005 is a DFI (Optimax, 3.0L) it will give roughly 45% improvement in mileage but is actually heavier than the old carbed 200.
What you will gain is ease of starting and IMO slightly smoother running with the EFI. The EFI is computer controlled so they are more complex than the old carbed motor but they have proven very reliable. Touch the key and go like a modern day automobile, no more choking it to start.
I doubt it is the Optimax at that price because it uses a different wiring harness and Smartcraft gauges $$$.
Labor counts for something, any warranty? If I read this right you would be out of pocket $5200, including the labor? If so that puts the actual cost of the motor at around $4800 to $4900 plus labor. Maybe a little on the high end.