You could contact a local university or college, ask who TAs the core econometrics (which requires a knowledge of stats and matrix algebra) and second year micro/macro/stats courses, and have them teach your son on a one-to-one basis. Undergrad programs in economics tend not to be overly quantitative until about third or fourth year. A high achieving undergrad student might enjoy teaching an enthusiastic young protege at an affordable rate. There are lots of interesting game theory applications taught in the core micro courses, and macro could introduce him to the basic IS/LM/FE and Solow models.
