.......don't know if the 270 heads make X more power and the costs per hp for that difference.
I think common sense should be the driving decision maker here.
Engine builds geared more towards the milder street applications, or moderate compression bracket builds using stock stroke cranks might tend to favor the 240's, while the higher hp "rowdier" combos, especially those with stroker cranks, should be able to exploit the added runner size and flow of the 270's.
In other words, if you're looking for a 550-600hp 446, the 240's make more sense.
If you're looking at doing something like a 700-750hp 505 or 520, then the 270's will get you there easier.
For the 600-700hp crowd, the choice won't be as clear, and which one you select might come down to what other components/criteria are being considered(for example, does it all need to fit under a flat hood?).