Work on vanguard rep by doing bounties and tiger strikes.. once you hit level 2 for vanguard rep, you can buy legendary armour. The helmet will cost 120 vanguard marks but everything else is 65. Max out on marks (100 is weekly cap) and you will get one piece a week. More then likely you will get legendary engram in the process of doing strikes, whether they are for your class is another story. Try to buy an exotic helmet from xur or you will have to save up one week to get the helmet. Everything I have I bought except for my exotics which I got as rewards for strikes.