Typically, bow mounted quivers hold 3-7 arrows, and back/belt quivers hold 15-25. I have personally owned a back quiver that could hold up to 60 (crammed in, but usable), but I haven't seen anything like it in a couple of decades. Ah, 1970's design...
Anyway, I can see a back quiver that holds @ 50 arrows as reasonable for runners that use bows to have, probable cost would be @ 300 or so, imo. As a former NAA instructor, I do have some rl experience with archery.