You can get an idea from DSC price list, but remember they guaranteed there parts and check them before they ship.
Dwight
http://dscmotorsports.com/
from they web page:
Blocks are guaranteed to pass magnaflux and pressure tests and are to be useable for intended purpose.
352 $125.00 / ea C
390 $150.00 / ea B
391 Truck Crank (Steel) $275.00 / ea C
427 (Iron) $250.00 / ea D
427 Steel $450.00 / + C
428 1U CJ and T-Bird $400.00 / + A
428 CJ 1UB or #A $450.00 / + B
428 SCJ 1UA or #B