Sorry I cannot help with your questions about selling your products or metals, as I really have not been much of a salesman of these metals.
I am sure other members will give you good advice on that.
In my opinion, the real cost is your time and how much time you take in educating yourself.
With time spent educating yourself, you can learn to recover and refine these metals with a minimal cost of supplies, (costs of chemicals) making some of your own reagents at times, purchasing second hand kitchenware for the lab, or making many of the tools, or equipment, starting out without spending much to melt a few ounces of gold like a three dollar melting dish, eighteen dollar torch head and some dollars on some flammable gas...
You can start a business with good education and almost no money.
Or
You can start a business with good intentions and a whole lot of money and no education or no ideas of what you are doing...
The real key or treasure map for the gold seems to be educating yourself.
The education of learning about these metals alone is worth the time studying, you will profit from the gained education in many areas where these metals are involved, even if you never picked up a gold pan, a beaker, or a melting dish in your life the education is where we profit the metals come along for the ride as far as I can tell.
If you jump in without spending the time needed to learn the basics, then you will spend way too much on scrap, not understanding its value, spend too much money on chemicals and lab equipment or furnaces you will not need, have one difficulty after another not knowing if you are losing more gold or money than your gaining, or even know where the gold or value is.
This is a field of study you can spend a lifetime at and only learn a portion of it because it is so vast, or you can spend less time concentrating your time in a specialized field of a certain scope of recovery or refining, either way, the more you learn the more you can earn or grow, and the less you will spend to get there.
So I say the question I would ask is not how much money to get started (because you could begin with a shoestring budget), but how much of your time are you willing to put into doing the work to learn these skills.
Depending on the type of scrap many times it does not make sense to try to recover the metal or try to bring the metal to a higher purity (take a 14k gold ring for example) it has a recognized value, and it can be tested for that value in gold, if you refined it to 999 pure (24k gold)and melted it into a button, you could find it harder to get full price for the gold content, most buyers cannot test the purity and would only pay you for what they can test the button to, so they then would only pay you for 22K gold. you would not make much headway there and if you had not educated yourself on what the scrap ring is worth, or you could not test the karat you could lose money both on purchase and on sale, not even considering the cost of refining... Again an education pays.
Marked sterling and coin silver also have a recognized value, sometimes whether to refine or not becomes a decision you have to make on your own from your own education. Some buyers are not always educated in the same way a refiner maybe, he may just buy your legally stamped silver or something he can recognize for its value, another buyer may have better testing methods and will pay you a higher price for it...
Refiners will usually always buy your silver or gold, what you get for it may be another question.
If this is what interests you, and this is something you are willing to devote your time to learning (a whole lot of time), and you do the work you will profit, the more educated you are the more you can profit, if you jump in head first you could endanger yourself and put holes in your wallet.
I say these are a skill that takes years to learn, just like any trade, like other trades the more you put in the more you get back, you can learn to be a good mechanic or just learn to do tune-ups, the more skill and understanding the more you can do or profit.
I also would not look at this as a way of making much money, at least not at first, or a way to pay the bills, there is a fairly steep learning curve (for most of us anyway), so I would not quit my day job just yet.
You may not make much money at the beginning but spending your time educating yourself can pay you well in the long run.
If I was wanting to sell some silver I would make rings, jewelry has a much higher value than the metals alone (100's of times more sometimes) I made a few rings out of my refined silver (although I took my refined silver and added copper to make the rings), although I have not tried selling jewelry, although it takes a bit of equipment and tools but if you like to work with your hands and can, I feel this would bring the most from your metals, solders, and soldering or other silver pastes or specialty items may be another way to get the most from your metals, well I not much help when it comes to selling metals as I like digging holes in the ground and burying my metals.