You can spend as much as you care to for a ball head, and I would opt for some of the more elegantly geared Manfrotto models before plunking down the cash for those Arcos things. IN ground where you are likely to sink, it can be worth the time to find some good flat stones to set your tripod legs on. Hang your gear bag around your tripod posts, and wait a short time to see if everything looks stable.
One guy suggested buying one of those pencil laser pointers, (about $20, from Harbor Freight) and attaching it to your lens with rubber bands. Shoot at something about 20 feet away, and review the image, to see if the laser point moved.
This is a good test to use in any camera store that will allow you to shoot tests with their equipment. There is no wind in camera stores, but that would tell if the support is quivering under the load. It's a good field test to tell you if you need to try harder.