Kind of putting me on the spot, eh? There are about a zillion guys that could answer this better than I. But I'll take a shot at most of it. I'll leave the hardness to those qualified to answer, my tester is a thumbnail.
Cost is a HUGE variable depending on the paths you take. You could work pretty much with just what you might find already in your home or shop and only add a decent mold to start. So the answer to initial cost could be anywhere from $20 to several digits of dollars. I would expect an outlay of about $150 to reasonably set up for one bullet, with only the cost of molds for additional bullets - unless you get into gas checks or
I would suggest you start looking now for a free or cheap source of lead (NOT wheelweights! for muzzleloaders). Roofing lead, plumbing lead, lead pipe, x-ray shielding, boat ballast....
Commercial ingots can be purchased from MidwayUSA, BuffaloArms.com, TheAntimonyMan.com, and others. Those ingots are of known purity and weight so you might want to start with those before trying the scrap sources. Shipping tends to be a little costly.
It's easy to get a pretty useless alloy when using scrap sources. My recommendation as to hardness is to get as near to pure lead as possible, easily scratched with a thumbnail, for conicals. You could use significantly harder alloys for sabot purposes but remember the intended use of your bullet. If the bullet is for hunting you will want good expansion which will come from the softer alloys. Pure is hard to beat but a little tin makes the melt flow and fill the mold more readily. For conicals certainly no more than a 2% tin alloy and preferably a bit less would be desirable.
To get into it cheaply here's my recommends:
You could use a large cast iron or thick aluminum kettle over a camp stove or similar heat source, but so far as commercial pots, the Lee Pro 4-20 melting pot - there is a bottom pour variation and also a ladle model - both about the same price. I recommend getting the larger size pot to achieve a move even mix that maintains temperature more consistently. From what I've read, if you want to go a little upscale on the pot, skip the Lyman version.
Lee molds with handles are a bargain if you can find a suitable one for your purpose. MountainMolds.com can make you about any mold your heart desires at a reasonable price but you would need suitable handles. Dan, at Mountain Molds, seems to be a very talented individual as well as a friendly person.
Lee Lube & Sizing Kits can be had for cheap in most common sizes. Lee will make most any size you would need for $25 to your door.
Lee Lead Ladle for stirring/skimming but if you plan to ladle pour, get the Lyman ladle or similar.
You might also want to consider an ingot mold for making conveniently sized quantities of lead, especially if you are into cleaning and melting down scrap lead. I have a second pot for that purpose.
A fluxing substance, of which there are many that work, to help in the purification process. Fluxing helps coagulate impurities and makes removing them a more doable prospect. Clean cedar sawdust added to the pot will work. There are many commercial fluxes available.
LUBE - a whole other world - but a good lubing method and material is mandatory. Everything from Crisco to Alox to custom made blends can be used with success. Super91 (Bob Bowers) has an excellent recipe for some great lube!
Okay, that is the essential stuff. You could go cheaper on the melting pot but I wouldn't recommend it. There are other things you will need, primarily a
WELL-ventilated work area. Also rags, bucket of water, plastic or rubber mallet, gloves, eye protection, a straight screwdriver, and aluminum containers (pie pans work) will/may be needed. Most of these are items you will already have. Get creative and save a few bucks - for example, if you have an extra aluminum muffin pan it could become a muffin ingot mold. :-) Of course you would want to clear that with the boss.
There is a lot I've left out, I'm sure. We need to get some of the talent from the GB bullet casting/swaging forum to fill in the holes. Be nice if Super91 or Mose would throw in some of their knowledge - both make EXCELLENT boolets for the muzzleloader.
My own produce is humble by comparison, but I've shot 5/8" 100 yard groups using the bullet pictured below and pan-lubed with a 50/50 Alox/alcohol blend.
