As an option, check Southern Automotive:
http://southernautomotiveengines.com/
Complete 428, single four barrel, 470 hp, $7900.
Complete 428, dual four barrel, 485 hp, $9400.
I agree with kobrabob here; unless you really, really know what you're doing, you might find it much more economical in the long run to get a complete package from someone who does. Been there, done that, got the t-shirt and receipts to prove it. Many folks on the forum have Bill's engines and he has a pretty good following. Of course, check out Mr Gessford, also.