You can get target load for usually $55-65/flat (250 shells) for the cheap stuff. That's 17.6lbs of lead shot which is around $40 unless you live really close to Hummason in Hamilton. Add on wads, primers, and powder and you are above the cost of factory ammo.
If you are looking for specific loads (handicap loads, heavy loads, spreader wads, premium wads, international loads, etc.) then handloading can be cheaper as specialty ammo usually costs quite a bit more. If you are after regular target load for skeet or trap then factory ammo is hard to beat for price.
As for hulls you need to find data for the specific hulls you are loading for. Different hulls are made in different ways with different internal diameters, tapers, and base wads (the one at the bottom the primer goes through). Generally if you are looking for inexpensive hulls to reload most people get Winchester AA or Remington STS. You can get them for usually ~$.05/each and they are good for a couple reloads. I generally toss my hulls after 2-3 reloads but have had some last 4-5.
As yomomma said buckshot and slugs are very economical to reload but only really if you cast your own buckshot or slugs. Moulds for those are pretty easy to come by but it's time and finding a source for scrap lead. You can cast your own small shot as well for target shell reloading but those use dripper style casters instead of solid mould blocks you pour into and are usually at least a couple hundred dollars. I reload 8, 9, and 12 pellet 00 buck and 7/8oz and 1oz slugs for 12ga. Comes out to around $.25/each with free lead or $.40/each with paying for scrap lead.
