Just to clarify, a ball head isn't a gimbal head. While you can get lightweight gimbal heads that sit on top of ball heads, and smaller gimbals (such as the Wimberly Sidekick,) they're two different things- gimbal heads have a point of balance and are great for tracking birds in flight, race cars and motorcycles. Ball heads are okay for those things, but not as easy to manipulate for large super-telephotos where even a 400/2.8, 600/4 or 800/5.6 can be easily moved by a single finger. Also, once you've locked one axis, you can smoothly pan. This is becoming less important as image stabilized lenses start to take over.
Wimberly is the king of full-sized gimbal heads, and any full-sized head capable of handling almost any super-tele (except that Sigma 500/2.8 monster, AFAICT) will run between $520 and $630 other than one manufacturer who makes or made a full-sized carbon fiber gimbal (don't recall who, I've only seen one and that was in a store, I think it was around $1000.) The sole exception is generally the Manfrotto 393 for about $175 which will support 44lbs of gear.
If you never intend to go with a big gun mated to a full-on pro camera with an L bracket, then for small lenses like a 200-400 or 70-200 and the like, the "sits on a ball head" and side mount gimbals are a cheaper choice.
My normal rig is ~15.5-16 lbs of gear when shooting with the super-tele and a flash, and I wouldn't trust it to a side mount, let alone a stacked head.
Unlike every $80-200 ball head I've ever owned, my Wimberly II is still going strong after ~5 years, and if I hadn't gotten it, I'd have gone with a RRS, Markins or Kirk. I've spent way more than the most expensive of those over the years on Bogen/Manfrotto, Gitzo and other ball heads that never lasted. If I was shooting smaller lenses constantly, then Acratech would also make my list.
Paul