* Brand and Model: A crate engine (new, from the manufacturer) from a high-performance brand like a Chevrolet Corvette Z06 will cost significantly more than a crate engine from a less expensive vehicle. Think thousands of dollars difference.
* New vs. Used: A used V8 will be considerably cheaper than a new one, but its condition and remaining lifespan are uncertain. Used engines can range from a few hundred dollars (risky) to several thousand.
* Condition: A rebuilt engine will cost more than a used engine in need of repair, but less than a brand-new crate engine.
* Modifications: Performance modifications (superchargers, turbos, etc.) add considerably to the cost.
* Where you buy it: Prices can vary between dealerships, salvage yards, and online marketplaces.
Therefore, it's impossible to give a single price. You could find a used V8 for a few hundred dollars, or a brand-new, high-performance crate engine for upwards of $15,000 or more. Expect to pay several thousand dollars for a reasonably good, used V8 in decent condition.
