FWIW...
even with caliban;s interpretation, instead of a pair of 6th level spells, you then throw one chained GMW for the bows, and then a couple of normal 3rd level spells for the arrows, 50 at a time.
its not quite as onerous as the two sixth level spells, but consider that in all likelihood these will be cast by a sentient caster the night before. GMW with extend and chain is only 7th level and lasts more than a full day. GMW extended is only 4th and lasts more than a day at the same caster level.
So it really does not matter whether he spent one 7th and three or four 3rds the night before for 15 +5 weapons (party of six gets a bow and a melee weapon each with 3-4 weapons to spare on throwing things and 150-200 arrows.)
The big deal is still a ton of +5 weapons and net +10 bow.arrows.
is your party gonna run out of 100 arrows in a day?