The best deal I have found is the hardware store in Hollywood! That was a few years back. Tried making some my self but my cost was close to the bought ones. Be careful where you place them, thy tend to grow legs and walk off! Not saying there are any theifs around!
Ace has them, both the single and double. Havent looked at them closely but make sure there is enough rebar so it doesn't drift. I got some good ones at that feed store on 17, just before Bees Ferry heading toward West Ashley.