Things that can help keep muzzleloading a bit cheaper.
-Buy tight weave 100% cotton or linen and make your own shooting patches and cleaning patches. Buy small quantities while finding your rifle's preferred patch thickness. Once found, cut the other stuff you bought into cleaning patches. You can save old worn out jeans, shirts, etc. and make cleaning patches too. Scoring a nice old linen table cloth at a yard sale would give you a lot of patch material.
-I don't cast my own projectiles, but it would save money in the long run.
-There are more lubes that are cheap, easy to make, and go a long ways than Carter had pills. Take your pick. Spit or plain old water for target shooting. Olive oil, render down animal fat, etc., mixed with bees wax from a local bee keeper for a hunting lube. I rarely shoot a conical and when I do I buy already lubed ones, but those can easily be lubed up yourself too after casting them.
-I feel an adjustable powder measure has to be purchased, if you don't already own a scale, both for safety and convenience while finding your rifle's preferred charge. Find the lowest charge that gives what you consider acceptable groups for target fun. Find an ethical charge for hunting. You could make your own powder measures after that for fun and/or looks, I like antler. Drill or burn them out with a hot nail (very slow but can be done).
-I bought a tube of TC anti-seize about 6-7 years ago for the nipple threads. It is a very small tube and is still 1/4 full or so. It takes very little to work. I barely snug the nipple when putting it back in. While I don't own an inline, I can see where a breech plug would consume much more of it. I like the Teflon tape idea.
-Cleaning I just use water. I've tried other cleaning solutions like TC #13, Birchwood-Casey #77, Hoppes BP solvent, they just don't work as fast as bucket of soapy water method. Sticking the barrel into a bucket and syphoning water in/out of the bore is much faster than wet patch / dry patch with a solvent. I also like how well syphoning water through the flame channel cleans it. Works great and no issues as long as you get everything dry when done. A patch lightly damp with water works fine for swabbing between shots and when target shooting I don't even bother with a second drying patch. Zero issues, just don't use too wet of a patch. Dollar store window cleaner is darn cheap and works fine too if it makes you feel better to have something that evaporates.
I've never tried a MAP solution (Murphys-Alcohol-Hydrogen Peroxide) but worry about something I once read. Hydrogen Peroxide supposedly can go where water won't...like into the threads of your breach plug. Not good for a traditional rifle that it never gets removed from. No idea if true, I'd love to see the breach plug pulled out of a rifle that was cleaned for years with water and one that was cleaned with MAP for years and compare. Not starting an argument and won't respond to one. Just a concern I have that everybody's going to have to live with lol.
-I do like to use denatured alcohol for both a water displacer and stripping the rust preventative back out of the bore. Been using the same half gallon for 4-5 years, still about a 1/4 of it left. Keep it in the original metal can and in a dark cabinet. Protecting the bore with animal fat has worked for many moons, a good coating to keep oxygen from getting to the metal will prevent rust. I think the folks that have problems simply don't get their bore as dry as they think before applying it. This method would save rust preventative cost and alcohol cost, although I would still want to make sure the flame channel was dry in some manner.
-If swabbing between shots, sometimes you end up pushing crud down and blocking the flame channel resulting in just the cap going off but not the main charge. Many just pop a cap after swabbing to clear it. This costs two caps per shot. Caps are cheap, but if you want to be more frugal you can turn your jag down a bit. Chuck it into a cordless drill and spin it on a flat file. Go slowly and check fit often on a fouled bore. Try to taper it a bit, smaller in the front. You're looking for a fit that will allow the patch/jag to go down the bore smoothly and then have the patch bunch up and pull the fouling OUT of the bore. I'm really not this frugal, but this is a cheap ideas thread, and turning the jag down in this instance will cut your cap consumption in half. As a swab between every shot guy I simply just prefer how well turning the jag down works and I do consume half the caps.
-Powder. If using real black, split the cost with some other shooters and do a large quantity buy. The more folks the cheaper it is for hazmat and shipping fees. Of course know your state's laws.