I think ball heads require greater bulk and weight to achieve rigidity that a simple pan/tilt head (assuming same material). If nothing else, for friction area on the ball. Of course, ball heads have their own advantages which may be more important to you.
Is the prism necessary or can you use a WL finder? If prism is necessary, than is it 45 or 90 degrees? Sounds like a dumb question except that the more the legs are extended (to achieve height) the less stable a given tripod will be.
For example, my Bogen/Manfrotto 3001 (precurser to the 190) with it's most basic head (I think it is called the 3d head) is usable at slow shutter speeds with my 500c and 150mm only when kept very low. Weighting down the tripod helps.
My favorite tripod for use with my 500c is my Tilt-all. I might hike with the Tilt-all, but I would not backpack with it. Carbon fiber is too expensive for me too.
Tripod light weight, good rigidity, low cost - pick 2.