The cheapest route is to use the stick-on lead wheelweights...which are as nearly pure, soft lead as you'll get on the cheap. There's a small percentage of tin, which is a good thing.
The problem is that there are zinc and iron stick-ons...along with a couple of unidentifiable metals and even plastics. Beware of these. If you leave a tiny bit of zinc in the metal long enough for it to melt...you may as well throw out the whole pot.
The test is to use a small pair of pliers to "mash test" the weights.
If you can easily mash a corner...it's lead.
The other bad news is that, lead wheelweights are being phased out in order to protect 2 dozen or so giant California buzzards and the children, etc. So, get'em while you can. Local tire shops will often give them away, or sell'em pretty cheap. They're usually mixed up with clip-ons...so you'll want to deal with a shop that'll let you separate the pure lead weights from the antimonial lead. Of course, the lead clip-ons make great hardcast bullets, so you may want to think about that. If you don't use'em, you can always hold onto'em for somebody that will. When they disappear, the price for wheelweight metal will jump sharply.