If you are worried about the cost of reloading, having 100-200 worth of smithing work makes no sense to me either.
The .38 is the champ for reloading costs, if that were my concern I would buy .38s and shoot them for a year and then see if I simply had to have a .45. If you want .45 ACP performance in a long colt, just buy .45 Schofield or .45 Special (aka .45 Cowboy) brass or cut existing long colt brass down. You will burn through a lot less powder that way, and not have to 1) pay to modify the gun, 2) ruin its value since I doubt many folks want a rimless single action for CAS, 3) deal with costs/issues of modifying a rimmed action to shoot rimless ammo.
Best of luck whichever way you go friend.
By the way, there is a .45 Schofield 1860 Army conversion on sale on gunbroker right now.