With some Economy Fares the maximum combined Linear Length of any two pieces of checked baggage is 273cm/107in but no one piece may exceed a Linear Length of 158cm/62in - in which case the other piece may not exceed a Linear Length of 115cm/45in.
So for a 30 gram serving of protein it would cost about $1 per day. From these two samples of protein powder I found that an acceptable price range for 30 grams of protein from protein powder is between $1 and $1.50 (assuming close to equivalent protein powder quality).
Protein powders and shakes, such as the ones on this site, can offer as much as 20, 30 or even 40 grams of protein per serving, which may be a useful tool for filling in the gaps in your nutrition, but on the other hand, you might not even need one depending on your current diet and exercise levels.