Well, I've gotten my engineering to 365 w/o mining a single bit myself (though some was donated by a friend). I got my goblin rocket launcher recently, and it's just awesome. I also have a little mechanical dragonling, which is level 73 when I summon it.
Cheapest way to level engineering is to level it with mining though. If you have the money to get the mats though then go for enchanting, you get some greens along the way.