default to a min price if we loose track of how much they wanted to pay

lms/djangoapps/verify_student/views.py

@@ -61,7 +61,8 @@ def create_order(request):
     donation_for_course = request.session.get("donation_for_course", {})
 
     # FIXME: When this isn't available we do...?
-    amount = donation_for_course.get(course_id)
+    verified_mode = CourseMode.modes_for_course_dict(course_id)["verified"]
+    amount = donation_for_course.get(course_id, verified_mode.min_price)
 
     # I know, we should check this is valid. All kinds of stuff missing here
     # enrollment = CourseEnrollment.create_enrollment(request.user, course_id)