I shoot the unleaded pellets in all calibers. 100 yards ain't gonna happen in .177 or .22. Maybe in .25, and only then if your gun happens to like one of the two offerings, Baracuda Green or GTO. One is currently 15 cents a pellet and the other 20 cents.
Why do you need to reach 100 yards to punch paper? If you're dead set on unleaded ammo, shoot within the distance the pellets are still accurate, say 30-40 yards for .177. The pellets are so light you'll get plenty of drop and wind drift to play with. .177 has the most variety of pellets and is the cheapest caliber; three to four cents per pellet is possible. Cheaper yet, shoot BBs at 5-10 yards; you can buy a new cool BB gun for what you'll save on each set of "buy three get one free" tins of unleaded ammo.