Hmm, I've never been asked this one before!
I'd probably go with hemp protein powder as it has some healthy fat in there, if I went with rice I'd add some ground flax or similar in just to add a little fat to the mix, oats might make things a little stodgy? But the other alternative like quinoa flakes, rice flakes etc would be the same. I'd like some 'green' added to it, but if it's got to be cheap, then most green supplements simply aren't cheap.
So maybe something like:
Hemp protein powder
Rice or quinoa flakes (or oats but I wanted to offer some variety)
(if you want to treat yourself) green supplement
If we're allowed one amino acid I'd go with either L-leucine or a branch chain amino acid (BCAA) rather than glutamine, although given the choice I'd go with the green supplement rather than the the amino acid.
You could swap the hemp for soya, pea or rice & add a little ground flax, even vary the 'flakes' so you have oats for a while, then rice flakes, then quinoa flakes etc
That's off the top of my head I'm sure someone can think of a better version than that?