Other than the price of the vehicle, the cost to fully outfit will probably be about the same. There might be a slightly less cost for the FJ Cruiser because there are more options for pre-built / bolt on parts, which means less custom fabrication (like a rear bumper for instance). However, the FJ Cruiser is essentially a coupe. It is smaller and has less cargo room.
I would take the FJ Criuser out of the equation, personally. For the cost, I would equip two 4Runners, or one 4Runner and a Taco. One can be more of a base camp vehicle, and the other can be used for day trips for study. This will allow you to carry more equipment in a more utilitarian way. Tacomas are one of the top choices for expedition and overland travel in North America. Since there are only two of you, you wont need the extra passenger room and can make better use of the cargo space.
There are a few companies out there that fully outfit vehicles for specific purposes like yours.
Adventure Trailers offers full custom conversions in Arizona. You can see some of their videos
here. The Nemo Tacoma is pretty impressive.
Overland Experts can also provide you with consultation on vehicle outfitting and mission specific modifications. Click
here. Those guys consult people like The Discovery Channel to film in remote places and trained drivers for the Planet Earth series.
The DIY approach is good if you have a lot of time for trial and error and going through multiple set-ups until you find the right one. These guys are experts and can accommodate your specific needs. Their job is to come up with solutions for; storing and accessing mission critical gear, equipping a vehicle that will do you right the first time so you can spend your time studying the wildlife and not worrying about your vehicle accommodations.
Another forum to seek help in this matter would be Expedition Portal. You can go to their forums
here. There is a Toyota FJ Cruiser, Taco, and 4Runner specific forum
here.
In addition, no roads is one thing, but no roads + snow is another. Fresh snow even on regularly traveled roads can make them unpassable for even the most heavily equipped vehicles and experienced drivers. There are outfitters that specialize in over snow/ice expeditions, but the vehicles are so heavily modified that they might not be good once you get down into lower latitudes where those modifications end up being more of a hindrance rather than an advantage. Your best bet there will be snow machines. You will be able to travel over the snow without worrying about sinking down into unseen obstacles and hazards. You will not be able to travel over 3 feet + of fresh snow without even a base road underneath for any kind of distance. Here is a good example of two heavily outfitted vehicles with expert drivers traveling over 2+ feet of fresh snow on a dirt road: Video
. Keep in mind, there is a road, and more than 4 people helping.
Also, the opportunity for you to drive off-trail (not just "off-road") in the USA is very limited. In most cases it is not just illegal, but environmentally irresponsible. Travel by foot is sometimes the only way. I do know that because of the nature and scarcity of wolves, a lot of time they are studied with the aid of helicopters for location purposes.