The SBC is the cheapest way to go. There is so much less you have to have to get it rollin. A decent used SBC shouldnt cost much more than a dollar per cube. And so much stuff was originally bolted to the SBC that if you choose wisely, you dont spend a lot of money on adapters. Also almost every accessory is cheaper. You save the computer/harness work, o2 sensors and bung installs in the exhaust, setting up the cooling system, air filter system, oil pan swap. That kind of stuff adds up!
Now the EFI system is fool proof and very reliable. Carbureted is more to tinker with. (Solution...propane on a SBC works very well for me. Very reliable and is cheap!)