Here are some ideas for ya':
use activated magic item (unlimited charges or constant) = 12,000 gp
use activated (1/day, lasts 3 hours) = 2,400 gp
command word (unlimited charges, 3 hours per use) = 10,800 gp
command word (1/day, 3 hours per use) = 2,160 gp
use activated (10 charges, 3 hours per use) = 1,200 gp
command word (10 charges, 3 hours per use) = 1,080 gp
All of the above items grant darkvision. Items that grant a constant benefit are generally in ring form. All of these items take up a worn item slot on the character.