[@Leslie Hall]
It could depend on how much magic is put in but the low-end being a radius of a few feet while the uttermost high-end range being a mile?  A whole city block (as in roughly 500 by 500 feet) could be the average.  Again, how long the 'pause' is being held for would increase the ongoing drain.  A few feet for an hour might be pretty petty change in comparison to a whole mile for a minute but holding a spell for an hour is in itself quite taxing.