I'm with David on this one. I'd use a geared head like the Bogen 410 (model 3275 in the US) and a macro rail like the Bogen 3419. I find that a ball & socket head is too hard to set exactly and has too many degrees of freedom for fine tuning composition at high magnifications. A geared head allows precise fine tuning of the composition. The rail then allows you some front-back movement without moving the tripod and messing up the composition. Not necessarily a cheap solution, but it's the best I've found, and there are probably cheaper macro rails used.

Lee