It sounds like the discussion is evolving but I thought 273's post was an interesting point....and absolutely true. Doing the math on this one, especially with ~$3.00 hi-test gasoline, you'd have to drive A LOT of miles to pay for the mods with MPG improvements.
That said, it OP is talking road trip...and in this case range is a big consideration. So I suspect that fuel cost isn't the only concern.
As for the original question, I'd look at the cost of a Magnum with higher compression heads, custom cam and EFI compared to the 5.7 Hemi. It seems like this might tip the scales toward the Magnum.
