Tire shops and service stations that sell tires have been the cheapest place I've purchased from for many years. I used to actually get 5 gal buckets for FREE back in my younger days, but that ended quite a while back. In my neck of the woods, one can occasionally buy COWW's for as little as 25 cents a pound, but prices are climbing. If you do all your gas buying and auto servicing at one place, that's your best bet, but you never know what you'll find until you go asking around. That's why they call it "hunting" for WW's instead of "finding" them! But it's really not an intolerable experience, and only our own laziness keeps us from finding good places to get WW's. And WW's will do fine for 90%+ of all our handgun shooting. I've considered getting a shot maker for shotgun, but haven't pulled the trigger on that one .... yet.
Second best source, and it's for very soft lead, is lead sheeting, which is more "catch as catch can" in my area. But it shows up and is good for ML'ers and soft, target loads with wadcutters, if you still shoot .38 revolvers. Plus, it can be alloyed with WW's and linotype (if you find it), to produce just about any temper of lead you might wish for. Linotype is seldom used these days in printing, so it's harder to find than the first two, but .... you never know until you ask! Scrounging lead is an adventure in itself, and the feeling of glee when you find a good stash really makes it worth the effort.
Oh! And when you find a good deal, stretch as far as you can, and get much more than you need! It seems that one's shooting tends to depend heavily on how much lead we have around! More lead = more shooting = better shooting = better accuracy and quickness with our guns. It's hard to beat that combination of qualities!