With the aftermarket now manufacturing good quality cranks for reasonable price's I would think the 428 cranks would come down a bit.
I have been watching for complete 428s and have found several complete running 428 powered vehicles in the $900.00 to $1500.00 range.
I wound up buying a 428 from the Lakewood Washington Pull-A-Part http://www.pullapartwa.com/PriceList.html
for $150.00! It was a bitch to get out but worth it. I feel the prices for these are inflated most of the time, especially in the current economy.
Now if I could just find a 427 S/O at Pull-A-Part!