I agree...... For the most part.
I'd say 600-1000hp.

But...... No easily attainable, cost conscious iron blocks.

I don't consider $4500 a cost effective option for someone who wants to build a reliable motor in that hp range.
The Brodix iron block is available in a multitude of configurations for $1995, and is perfect for that type of build.
Want something a little fancier? Dart Big M for less than $3000.
A 588-632 combo with a big set of cnc ported conventional heads will easily make over 900hp.......... And you could have all the parts to build the complete motor at your door in a week.