Hard to find more protein per dollar than $2/lb of canned chicken with an equal or even similar Protein Digestibility-Corrected Amino Acid Score (PDCAAS).
eggs and milk are generally cheaper per gram of protein, and both have the same PDCAAS as chicken
If my numbers are right, you could undercut that slightly with combo of pulses/tofu/rice, albeit with higher calories/carbs depending on mix.
edit: seeing the same as lantry, that eggs or milk are cheaper animal source