Books and or a video are a good way to see whats invloved, rifle, fowler, musket the process is all pretty much the same.
The "Gunsmith of Grenvile County" by Peter Alexander, or "The art of building the Pennsylvania longrifle" by Dixon, Ehrig & Miller are a good place to start. I've never owned a video on building, I'm always leary of some videos as they make it seem to easy, I mean ever see Norm scerw up a project on New Yankee workshop? No matter which a book or a video is a very good idea to show you what's involved in building a muzzleloader.
There are less expensive kits, some web sites to look at for idea's is Track of the Wolf, Pecatonica Long Rifle Supply, etc.
Just for an example you could do a 20 ga. Northwest Trade gun for around $600.00 + sh. Not cheap but, less then a Chambers kit
The other thing you have to look at is tools. A simple kit like a Cabela's hawken will only require simple tools, files, screw drivers, maybe a small 1/4" bench chisel, sandpaper, etc.
Something like a trade gun you need more tools, a cabinet makers file, some small gouges, bench chisels, taps for cutting treads, drill bits, a counter sink, a torch & solder, assorted files, sandpaper, etc. While not necessary having access to a drill press is nice when it comes time to drill the barrel tenon holes and the touch hole.
The other thing you need is patience! (Something very lacking in this instant gradification filled world) Try using short cuts like a dremel tool for inleting, or a belt sander or random orbit sander for stock shaping, an angle grinder to fit the breech plug, or any thing else to "speed up the process". And you can end up with a barrel shaped fence post and a gun stocked shaped hunk of fire wood!