Remington did supply steel barrels but by no means were they all steel. Not everyone even wanted steel barrels...
From and October 1860 Advertisement:
Cast steel barrels of 6lbs wt. or less, each $3.00
............................over 6lbs, extra per lb. .40
Iron barrels, 7 lbs wt or less, each $2.00
..................from 7 to 12 lbs, extra per lb. .10
..................from 12 to 18 lbs,.............. .20
Also offered were false muzzles, cylinders for rifling machines and rifle telescopes.
...and so on like that. They also offered "Stub Twisted" barrels and a variety of matched barrels for double guns. Gain twist rifling any barrel was $2.00. They offered custom-made heavy barrels and what must have been huge barrels for punt guns. The only complete guns that were available were their cane gun and the Beals and Rider patent revolvers. The only complete long arms they had made to that point were the Jenks patent carbines for the navy and some M1841 Mississippi rifles.
The term "cast steel" does not mean that the barrel was cast. It refers to the manufacturing process by which the steel was made. Part of the reason the costs were greater was that virtually all steel was imported where iron could be obtained domestically. Remington barrels were made from a bar about 9" long with a 3/4" hole through the middle. This was heated and run through a series of rollers, always with a mandrel in the hole, that stretched the barrel out while squeezing the bore smaller.