Darrin,
If you insist on a NE caliber and don't want to pay the $8500 that it would take to have Butch Searcy build it for you, then the best thing you can do is go to www.auctionarms.com or www.gunsamerica.com and stay on the lookout for a seldom fired Pedersoli in 45/70. Several double rifle shooters have taken such a piece, which seems to run around $15-1700 used and had it rechambered for either .450 NE or .450 #2 (which will have much lower pressure). That costs around $250-300. Oddly enough, they have proven to shoot accurately without re-regulating. This is against all lore, expectation, good sense and probablility but it is the case. That will give you a DR for about $2300. Then, if it doesn't regulate to your satisfaction, you still have a grand to get it redone. Of course you do have to appreciate hammers . . .