The loads on rudders are huge. $5k for a boat with little to no extras, no motor? and a hack job of a rudder (sorry) is too much. How is the trailer and sails? How many sails? How's the running rigging? You can get a nice boat for 5k these days.
3.5hp is all you'll need for that boat.
Merit 25 # 764 "Audrey"