When I brought Rascal home last May - this is what he looked like as a yearling:
He felt even worse than he looked. The hair hid his ribs, but you could easily feel every one and his hair just felt gross. He was also very tiny - only 12.2 hands.
I didn't want to over do his system so I started him on good clean local grass hay, some pasture time and alfalfa pellets. Oh, and a free-choice mineral block. A very simple diet, yet it had a good amount of protein from the alfalfa.
A little over one month and a good bit of weight later:
We eventually switched him over from alfalfa pellets to safe choice and he is still on that. If possible - check out your local feed stores to check prices. One of my local feed stores carries alfalfa and safe choice both for several dollars less than TSC.