I don’t know how waterproof it is, but the Lowe’s iris second-generation keypad made by Centralite is popular in the community here. You could ask in that thread for how sheltered it needs to be.
It cost just under $40, and you can typically find a Lowe’s coupon to bring that down another 10%. It gets low ratings on the Lowe’s site because the first generation keypad included a door chime and the second generation does not and people are mad about that. But it seems to be a reasonable device when looked at on its own. (Only the second generation will work with SmartThings).
http://www.lowes.com/pd/Iris-White-Security-Alarm-Keypad-Works-with-Iris/999925326
You could also mount it inside a clear plastic box with some air holes, that’s pretty common for security keypads. Just don’t get a metal enclosure or you’ll have trouble getting signal through.
