I understand your issue, I have it aswell. You need to sell an insane amount of copper tools to reach tin and it isn't purely based off the price of the ingot because you need to factor in the grips and guards, if used, in a part. And ontop of that the prices aren't as exact as they claim to be. The player card that indicates skill points, activated by pressing "P", shows that the base state of charisma gives you a 10% boost of sale prices for a total of 110% money gained from what you spent on making the part. However, if you look at the board on the left wall, inbetween the doors to your bedroom and the forge, it shows all of the prices customers paid for the parts and they almost NEVER match what the skill card indicates. Its still random, you can even LOSE money sometimes for no reason, the customers simply don't pay the right amount. I've had a customer pay $56 for a copper great sword, which used 3 copper ingots, a fancy 2 handed grip, and a 2 handed guard for a total of about $40 give or take, and I've also had the same sword sell for only $24.
It may be possible that the prices depend on how fast you give the items to the customers but I know for sure this system is properly coded yet. Which, in my opinion, is perfectly fine for now because it is still very early in development but it does slow down the progress tremendously and leaves money gain to chance.
Check that board for sale prices you get and monitor to see if time is directly related to the price of a weapon or not and let me know, I'll be doing the same. All I know is that I think the charisma state increases the MAX profit rather then the ACTUAL profit, for now.