That's the going cost of the 5.3's these days. They're heavier than LS1's by about 65lbs, and smaller displacement by 0.4L, and the cost of an LS1 is dropping every day, so these engines are not to desirable to those that want big NA power.
Nice thing is they're an iron block, and the amount of money you save by getting a complete engine for $200-400 leaves plenty of turbo $$ to put to shame all those other people out there who wouldn't be able to stand having a non-all-aluminum gen3/4 engine under their hood!