Plus front shocks ($150 used), plastic ($400 new), lights, wiring harness, CDI ($150), brakes, rear sprocket, oil tank, coolant overflow tank, air filter box, battery ($120 new), etc.
The going price on a slightly used 450 engine minus carb, pipe and electronics is $3,500. I've seen a blown one sell for $2250 on ebay.
If you're looking to build a YFZ from these parts, you're better off buying a used 2004 for $4500 - $5000.
If you're looking to build some sort of hybrid, then it's a pretty good deal.