If you are talking "old school" big blocks, they are primarily boneyard or swap meet items. There are a few retail engines available already built to the max and ready to drop in but you can easily invest 9k to 12k to start.

I think there are some "truck" tall deck 427's that you can build to suit your needs, once again they would be found in the boneyards/swaps. Haven't researched these but have heard of them.