Look at a Gitzo 12-series ball head- they have them in traditional and off-center ball configurations. I have one (the 1245 I think is the model #) with the off-center ball, and the quick-release. I have used it for my Hasselblad system as well as my Shen-Hao 4x5, and it has been more than up to the job. It's one of the magnesium-alloy ones, so it is quite light, and I'm pretty sure I paid less than $250 for it. Look at what Henry's has for sale on Ebay- they sell off a lot of good Gitzo gear for very reasonable prices - most of it new in box, or in-store demo stuff, so not too badly used, and frequently cheaper than B&H.