Remington never called any gun the "Model 1858." There were three Army (.44 caliber) revolvers with the 1858 patent date. The earliest was the Beals' Army, which is marked "Beals' Patent Sept. 14, 1958 Manufactured by Remingtons, Illion, N.Y." In about 70% those are bringing around $3500 for the commercial model, about $1000 or 1500 more for the martially marked.
The later Model 1861 also had the 1858 date and was marked "Patented Dec. 17, 1861, 1858 - Manufactured by Remingtons, Illion, N.Y." Values run about the same.
The New Model Army is the one erroneously called the "Model 1858" and is the one usually copied in modern reproductions. It has the 1858 patent date, but is also marked "New Model", although some early ones lack the latter marking. They are the most common, some 136,000 having been made (serial 12,000-148,000), and bring only about $2800 in 70%, with 15% additional for martially marked.
HTH
P.S. The New Model Army, because of the large number of reproductions, is also the one most faked, so buyers should the "emptor" would do well to "caveat."
Jim