I have experience with two outfitters I know have long range shooting experience.
John Porter of Morning Creek Outfitters is very well versed in long range shooting and hunts country that can require it. John can also do late season trophy hunts with a real opportunity at a 350 class bull. These hunts are expensive and require long days on horse back but if you enjoy serious backcountry hunting this is the ticket.
Ray Milligan also knows what he is doing and has taken elk out to 1000 yds himself. He has the ability to supply landowner tags in New Mexico so it is a guarantee you will get a tag if you book with him. The bull I took with him in 2003 was #900 in 6 years. He has a 75% success rate year in and year out. www.milliganbrand.com
I realize this post is about a year old, but I am new to the site and just came across it. As Mr. Burns was referring to Mourning Creek Outfitters, and John Porter, I can also attest to his statements. I myself have elk hunted with John, up around BEAUTIFUL Sunlight Basin, I personally took an elk @ 350 yds, not real long but that was when I first started long range at all. My father, using one of John's custom built rifles, shot one @ over 800 yds. Not only can you look forward to taking long shots with John, but you can do it with confidence. He is an accomplished Nat'l Guard 1000 yd shooter and knows the mountains of NW Wyoming as well as anyone around. But be ready to put some effort forth. If you do a 350" bull is within your means. John also hunts some of the most beautiful areas in North America; Sunlight Basin, Crandall Drainage, Beartooth Wilderness and many others, all very wild, and "Western".
I hear that Hells Canyon of the Snake in Idaho is the kind of place where you can see trophies every day but have trouble getting into normal hunting range. I have seen horns that people have brought out of there and they were impressive. Idaho is also cheap to hunt and you can always get a tag. Also requires long days on horses in very rugged country.