I disagree that MFS supply and bargain locks are good. I'm a Realtor, and have had trouble wth the boxes i got through them (or ones left on my listings with their logos on them). You can dial the correct code and they jam and won't open, especially in humid weather.
NVMS now has a store, and they have lockboxes alpha and numeric for 10.95 each (I haven't had trouble with these), and locksets at 4.75 and down, based on quantity.
I think their free shipping is at a $500 order.
I deal with Jason there, and he's been very helpful and informative. Ask for him, if you can! And no, I am not affiliated with them in any manner, other than my husband having done some work for them and us placing orders...http://www.fieldservicewarehouse.com