Wiper motor really isn't that big of a deal. Since you say it works sometimes I would guess the most likely source of the problem is the ground. Can be solved in 5 minutes by routing the wire from the motor to the engine grounding point on the firewall. Even if the replacement is the only option the job is not difficult. 3 bolts from the engine compartment and one nut from the underside of the dash on the passenger side. Half an hour project if all goes well.