Nrgy, I've got some good news and some bad news. Actually, you might like it all.
Gotta think outside the box here.
First of all, 400 miles is no trip for a helicopter. You're going to spend well over two hours in even the fastest helicopter. And you're going to need a pretty big helicopter if it's you, your brother, your parents and baggage. So the EC120 is out right there. MD600 can probably take four+bags and full fuel (where *do* you put the bags?), but even so it only goes...what...120 knots? VFR? How much torture do you want to subject your parents to?? Plus, with weather and terrain considerations in that part of the country, you absolutely positively do not want to do this trip while being limited to VFR. The 109 could probably do it IFR and pretty fast (for a helicopter), but you might still have to stop for fuel because I'm not sure it has the endurance for a 400 mile flight with IFR reserves (could be wrong there though).
Here's a better idea. The initial cross-country is an airplane trip, plain and simple. So buy a Beech Bonanza with the RR/Allison B-17 turbine. Somewhere around $800-900k. You and your brother can fly it, and you're both probably insurable in it. Two hours in the Bonanza.
Or, go up a notch to the Socata TBM 700/850. These start around $1.5M. No way will any insurance company touch you guys in a twin-anything, and anyway the only twin I'd recommend would be the baby King Air 90. I mean, don't even bother with piston twins. Or singles for that matter, but that goes without saying.
At the Montana end, buy a $600k Bell 206B or EC120 and stick it a hangar there for the times you need it when you're there. (Hangar rent might be cheaper for the Bell.) Shouldn't be a problem with insurance if you factor in $10k for Bell school.
Your total aircraft purchase will be under $2.0 million. Operating cost of the turbine Bonanza will be a WHOLE LOT LESS on a 400 mile trip than a helicopter. And you still get to fly a helicopter around Montana if the weather's nice (which is the only time you want to be flying a helicopter, trust me).
Best of both worlds!