Sounds about right.
For the cost of the KB 400cid slugs and a balanceing, he could be up and running quick and cheap (Except pistons cost. What was it?)
The extra work of the crank can depend on cost. It is a widely vaiable cost. Just things like where you live, one machinest vs. another, material of crank, int. vs ext. balance. Machining journals down. etc..
While it COULD be done cheaply, I've never done the homework on it. Fast01 ditched his 451 w/cast crank in a heart beat flat and redid his entire engine over. The 451 set up is collecting dust right now. (Hummmmmmmmmmmmmmmmm...evil thoughts.....)