Depending on whether or not your joint have any tin already on them or not, if you went over to your local hardware store and picked up a one pound roll of 95-5 solder, then mixed it all in with your 50# of lead, you would end up with roughly the following,
Tin 1.86% Antimony .10% and Lead 98% which would give you a VERY good alloy to pour up bullets with and would run close to a 9 BHN in hardness.
So for the cost of the roll of solder, your lead, and some time to smelt it all into ingots, you would be good for around 2300 bullets at approx. 150grs.
I realize that lead is hard to come by, but if you can't find it locally, look on the classifieds of different forums. There are usually a couple of folks who post up range lead or clip on wheel weight lead and usually it has already been smelted into ingots ready to cast with. Most of the time it can be had for around a buck a pound, or $65-70 per medium flat rate shipping box, shipped to your doorstep. If you purchased one box of wheel weight alloy for $65, then mixed it 50-50 with your pure sheeting, you would have 100 pounds of the following alloy at right at a 10 BHN,
Tin .25% Antimony 1.25% Arsenic .13% Lead 98.1%
The range lead will run fairly close to the wheel weights, but it still really needs some tin added.
If you added in a 1# roll of solder it would help a lot, and if you mixed the whole 65 of wheel weight to the whole 50 of pure you would have the following.
Tin 1.10% Antimony 1.72% Arsenic 0.14% Lead 97.0% Total weight of alloy 116.0 # at a 10.5 BHN
If your just pouring 148gr WC's you would end up with around 5400 bullets.
I went through a whole lot of figuring cost when I started out. I figured in my time spent going around to one shop after the next, to the scrap yards and so forth, along with fuel as well. It was MUCH cheaper for me to simply purchase mine and have it delivered right here ready to cast with, than to hunt it down and then still have to smelt, clean, and pour it into ingots before hand. I still take what I purchased and smelt it into my own ingots as this allows me to flux it a couple of more times. Then I know when it goes into my casting pot it is about as clean as it is going to be.
Oh one other thing, I know you SAID your were only going to cast MAYBEEE just wadcutters, but I have to tell you, once your set up and have alloy, your mind will start working on you and before you know it your fighting a loosing battle. I don't think crack will get you as fast as casting will. I know it's only one little mold, then two and then one day you look up and it is now a dozen or so, and your mail person hates you because they have to carry those darned heavy boxes up to your door, and then, and, and....
Ohh sorry guess I got a little carried away....
Hope this helps...
Oh one last tidbit of knowledge-- when you DO start to put your alloy together weigh the different amounts and write it down. It will be a valuable tool two months or more down the road when you finally decide to make it up again. Or if it is a wash, you will know what NOT to blend together.