Probably not what you're looking for, but computer programming. The more advanced an ME gets with that, the better their job prospects. CAD, FEA, Labview, C+
I've drawn some stuff in CAD that I can make for my car using parts from McMaster-Carr (Google it if you're not familiar) for not a ton of money. There are cheap way of getting the metal cut (i.e. water jet) and then the most expensive thing would be welding.