Before going Legendary I would buy the level 30 sodas each chance I got. Put them in storage and sell them when I needed money. I also used them when I hit level 30. After upgrading I sold them for cash back (though reduced).
What you do is when you reach your cap of money go to either watchtower/hall of doom and go to the little kiosk vendors (the ones that sell only styles and are not from NPC.)
They are in the center area of the hall of doom, not sure about watchtower. And buy the styles that you need to collect.
Each one cost some where from 100-400. You can have all of them or close to all of them by LVL 30.
After you collect, sell stuff you don't need. If you reach your limit and not put much into escro and have a pretty full inventory to sell stuff you can get lots of styles and feats for styles! Also rather than selling stuff you can go to the mod stations and salvage items for materials rather than selling them for when you reach lvl 30 and end game for mods for your gear.