Used 5.7L truck motors are $1500.00 to 2500.00
Used 5.7L car motor are a bit more
Used 6.1L motors are typically in the $4,000.00 to $5,000.00
Used 6.4L motors are still pretty rare, I found a new one on ebay for 7K
Hope this gets you started.
Regards,
Joe Dokes