Amazon has the Design House Plaza Locking DoorKnob (Stain Nickel, 728204) on sale for $8.50 with free shipping on $25+ or with Prime.

Works for left or right hand doors. Adjusts for 2-3/4" and 2-3/8" backsets; Fits 1-3/8" and 1-3/4" thick doors. 2 faceplate options.