If shooting lead bullets and using iron sights, for the money I doubt you could go wrong with the Deerstalker or Great Plains rifle from Lyman, depending on whether you want to shoot (respectively) Maxi- or Minie-style bullets. Being right-handed but left-eyed, I shoot long guns left-handed. Years ago I managed to find two left-hand replica Hawkens, manufactured by Investarm in Italy, a 58 cal. from Cabela's and a 54 cal. Great Plains from Lyman. The 54 cal. had to be sporterized by squaring off the rear stock and installing a recoil pad; the 58 cal. came already so sporterized, as does the Deerstalker. (This alteration works with heavy bullets and safe maximum powder charges, as a curved crescent metal buttplate can be murder on rotator cuffs in heavy recoil.)
On both rifles I installed studs for sling swivels and Lyman 66 aperture rear and so-called fiber-optic front sights, and replaced the wood ramrods with synthetic "unbreakable" ones, using a metal range ramrod when sighting in at the range. Shooting with set triggers Hornady Great Plains hollow-base/hollow-point swaged bullets (425 gr. in 54, 525 gr. in 58) with charges of Triple Seven powder 10 gr. (by volume) below maximum loads specified by the manufacturer, off a benchrest the rifles give one-hole groups on paper targets at 50 yards, about the farthest shot I can expect in swamps where I hunt. I take the 54 for deer-only hunts, and the 58 if I have permits for both deer and hog. My bullet casting for rifles is so far pretty much limited to 45-70, and I wonder whether pure lead bullets cast from the Minie bullet moulds I have would equal the results I get from the Hornady bullets. Also, Triple Seven cleans up just fine with Simple Green and boiling water. I'd never go back to FFg blackpowder unless nothing else was obtainable.
Aperture sights on muzzleloaders are nothing new. The German Museum for Hunting and Fishing in Munich has on display 18th century flintlock hunting rilfes so equipped.