also once you progress further in the companions you can forge ancient nord armor and nord hero weapons at the skyforge

btw training cost depends on your level, the higher your skill level the higher it costs to train...you didnt think mastery would come cheap did you?

If that's the case then making swords is the best way to go. They fetch a good price and require far less materials than a cuirass.

As it has been stated already, post-1.5 smithing is weighted on quality rather than quantity. Smithing high-value items boosts your smithing skill (MUCH) faster than smithing low-value items (eg. iron daggers pre-1.5). I've found jewelry to be a good method (and not just gold or silver rings as those have hardly any value, emerald and diamond rings are much more effective).

Ultimately, smith the highest value items you can (providing you can get your grubby hands on the materials). Just take a look through the items at the forge and figure out which ones will give you the best bang (item worth) for your buck (cost of "ingredients").