Leaves $239.21 to buy a metal GTO tank and get the welding done. And there were plenty of cheaper options for a stock tank so this isn't even the cheapest way to do it.
Full disclosure, I did this back in 2017 and was actually for the Magnum EFI I had planned to use. I wouldn't be surprised if the Tanks Inc EFI tank was just coming out or wasn't out at the time. I know the Stealth setup was out but pretty sure it was over $500 at the time.
And I don't like the Tank Inc "baffles". Much prefer the syphon setup of the GM bucket that keeps the bucket full at the same time it is supplying fuel to the engine. You could have a 1/4" of gas sloshing around the bottom of the tank but the GM fuel module bucket would be overflowing with fuel.
And if I was looking for another way to do it, I wouldn't do a Tanks Inc tank. I would use the Holley setup that fits into the stock tank mostly because of the HydroMat pickup. I've heard reports that it works well, but haven't done it myself.