Jrkd,
www.krepower.com These guys will sell you a motor ready to go carb to pan and are relatively close to you. The reason why you see the builders rebuilding used motors is that the last 400 pontiac v8 was produced in 1978 and was last available in 1979. If you want a "new" block you will have to go the I/A route. These blocks can cost from $3200 on up. That is if you can find one.