That particular rifle, whether a "JM" marked or "Remlin" is a pretty hard sell around here in the Central Texas area. The "JM" Marlins usually sell better/easier than the Remlins, but still, they tend to linger on the local gun boards unless marked low/very low. I remember last year one guy sold his NIB Remlin for $350.00 and it sold within minutes. The .45/70 caliber is legendary, and would easily kill any animal on the North and South American continents. However, people are intimidated by the stories of its stout recoil, and the price of the ammo. (BTW - I hunted with an experienced shooter last year that was a Guide Gun fan, and he compared the recoil as being comparable to shooting a 12 ga. shotgun with slugs.) The rifles are neither target guns nor range rifles. A lot of people I know like to use them for hunting hogs.
I think the estimates provided by Rastoff and hkcavalier are accurate. At my age, I've decided to keep and use the rifles I have on hand and not acquire any new ones for my family to worry about once I pass - however, I do know my son has been drooling over the thought of owning a .45/70 for a long time.
BTW, the earliest Marlin Guide Guns had ported barrels. Now a days, on the more modern versions, the only barrel porting you'll see is done after it leaves the factory.
Good luck,
Dave
